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WO2003038487A2 - Improvements in and relating to optoelectronic devices - Google Patents

Improvements in and relating to optoelectronic devices Download PDF

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Publication number
WO2003038487A2
WO2003038487A2 PCT/GB2002/004993 GB0204993W WO03038487A2 WO 2003038487 A2 WO2003038487 A2 WO 2003038487A2 GB 0204993 W GB0204993 W GB 0204993W WO 03038487 A2 WO03038487 A2 WO 03038487A2
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WO
WIPO (PCT)
Prior art keywords
optical device
manufacturing
body portion
optical
dielectric layer
Prior art date
Application number
PCT/GB2002/004993
Other languages
French (fr)
Other versions
WO2003038487A3 (en
Inventor
John Haig Marsh
Ann Catrina Bryce
Bocang Qui
Elchuri Rao
Bertrand Theys
Yvon Heymes
Original Assignee
The University Court Of The University Of Glasgow
Centre National De La Recherche Scientifique
France Telecom Societe Anonyme
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Publication date
Application filed by The University Court Of The University Of Glasgow, Centre National De La Recherche Scientifique, France Telecom Societe Anonyme filed Critical The University Court Of The University Of Glasgow
Priority to AU2002337368A priority Critical patent/AU2002337368A1/en
Publication of WO2003038487A2 publication Critical patent/WO2003038487A2/en
Publication of WO2003038487A3 publication Critical patent/WO2003038487A3/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/182—Intermixing or interdiffusion or disordering of III-V heterostructures, e.g. IILD
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/322—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections
    • H01L21/3228—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections of AIIIBV compounds, e.g. to make them semi-insulating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/324—Thermal treatment for modifying the properties of semiconductor bodies, e.g. annealing, sintering
    • H01L21/3245—Thermal treatment for modifying the properties of semiconductor bodies, e.g. annealing, sintering of AIIIBV compounds
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12097—Ridge, rib or the like
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12128—Multiple Quantum Well [MQW]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/3413—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers comprising partially disordered wells or barriers
    • H01S5/3414—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers comprising partially disordered wells or barriers by vacancy induced interdiffusion

Definitions

  • This invention relates to a method of manufacturing optical devices, and in particular, though not exclusively, to manuf cturing of integrated optical devices, optoelectronic devices or photonic devices, for example, semiconductor optoelectronic devices such as laser diodes, optical modulators, optical amplifiers, optical switches, passive waveguide devices such as mode expanders, compressors and converters, and the like.
  • the invention further relates to devices made by such a method, as well as to Optoelectronic Integrated Circuits (OEICs) , and Photonic Integrated Circuits (PICs) , including such a device or devices.
  • OEICs Optoelectronic Integrated Circuits
  • PICs Photonic Integrated Circuits
  • PICs Photonic Integrated Circuits
  • a fundamental requirement for PICs is the realisation of low-loss optical waveguides to link different components to form a functional circuit.
  • the semiconductor materials forming an optical -waveguide absorb -light through three principal mechanisms .
  • the first is fundamental edge absorption (FEA) due to a carrier being excited across the band-gap by absorbing a photon (band-to-band absorption) .
  • the second loss mechanism is free-carrier absorption (FCA) , due to electrons and holes moving in response to the electric field of the light wave ' and losing energy through scattering collisions.
  • inter-valence band absorption is associated with the presence of free hole transitions among- the heavy-hole and spin-orbit split-off bands, and is directly proportional to a concentration of holes in the valence band giving rise to an absorption coefficient at least 7 to 8 times larger than that of FCA.
  • FEA is the strongest absorption mechanism.
  • Quantum Well Intermixing is a post-growth technique that can be used to modify selectively the profile of a Quantum Well (QW) , leading to a "blue-shift" (ie a shift towards shorter wavelengths) of the optical absorption edge.
  • FEA can thus be reduced to a minimum by using QWI to widen the band-gap of passive waveguides.
  • Quantum Well Intermixing techniques There is a variety of Quantum Well Intermixing techniques . Some of these involve the diffusion of an electrically active impurity into the semiconductor, which may be either a donor or an acceptor.
  • One mechanism by which the impurity can induce intermixing is by the so-called "Fermi-level" effect. Since the presence of the dopant species influences the position of the Fermi- level, there is a resulting change in the concentrations of charged point defects in the semiconductor. This happens partly because the point defects in semiconductors are charged and themselves behave as donors or acceptors .
  • the diffusion of the point defects - particularly lattice vacancies, but also interstitials providing there is some exchange between lattice atoms and interstitials - is then responsible for QWI.
  • impurity species eg zinc in GaAs
  • some impurity species diffuse as interstitials hop into and out of lattice sites (the so-called 'kick-out' mechanism) .
  • This process can result in QWI.
  • impurity free QWI processes in which the point defects are generated by other means . These techniques include illumination by CW or pulsed lasers, or annealing samples with a suitable dielectric cap on the surface in which lattice matrix elements can dissolve so generating vacancies . In all cases the point defects behave as donors or acceptors .
  • QWI arises from the diffusion of point, defects or from impurities.
  • the point defects are charged and have free electrons or holes associated with them.
  • Impurities and/or structural defects responsible for QWI are also usually charged and have free electrons or holes associated with them.
  • FCA is proportional to the concentrations of free electrons and holes in the semiconductor layers; therefore to reduce FCA in thermal equilibrium the concentration of the majority carrier (electrons in n- type material, holes in p-type) should be lowered.
  • IVBA depends only on the hole concentration so the contribution thereof to the total optical propagation loss is reduced by lowering the hole concentration.
  • the optical overlap with the waveguide core is around 50%.
  • Generally around 25% of the optical field extends into a p-doped waveguide cladding layer, in which the hole concentration typically lies in the range lxl0 16 crrf 3 to lxl0 19 crrf 3 .
  • FCA and IVBA make contributions to the optical propagation loss. The magnitude of the loss depends strongly on material composition and the optical wavelength.
  • a method of manufacturing an optical device including the steps of :
  • passivating or “passifying” is meant neutralising the electronic activity of the dopants and/or point defects .
  • the dopants may preferably be p-dopants, but may instead be n-dopants or indeed may be both p- and n- dopants .
  • Step (a) is most preferably undertaken before step
  • step (b) in a variant step (b) may be undertaken before step (a) .
  • the step of intermixing at least part of the Quantum Well (QW) - Quantum Well Intermixing (QWI) - may result in any effective increase in band-gap of a region of the device body portion providing the Quantum Well (QW) structure .
  • the step of passivating at least dopants within the device body position may act to reduce optical absorption within the device, particularly absorption via IVBA.
  • the method of manufacture also includes the preceding steps of : providing a substrate; growing on the substrate : a first optical cladding layer; a core guiding layer including the Quantum Well
  • the method may also comprise the step of growing on the second optical cladding layer a contact layer.
  • the contact layer may, in use, serve to protect the second optical cladding layer, eg from Hydrogen (H) or Deuterium (D) .
  • the first optical cladding layer, core guiding layer, and second optical cladding layer and optional top contact layer may preferably be grown by Molecular Beam
  • MBE Metal Organic Chemical Vapour Deposition
  • MOCVD Metal Organic Chemical Vapour Deposition
  • the Quantum Well Intermixing (QWI) step may include the step of: depositing a dielectric layer on at least part of a surface of the device body portion so as to introduce structural defects at least into a portion of the device body portion adjacent the dielectric layer.
  • a method step is disclosed in GB 01 01 635.1 of 23 January 2001 (published as GB 2 373 148A on 11 August 2002) also by one of the present Applicants, the content of which is incorporated herein by reference .
  • the structural defects may include "point" defects.
  • the dielectric layer is deposited by sputtering.
  • the dielectric layer is deposited by sputtering using a diode sputterer.
  • the dielectric layer may beneficially substantially comprise silica (Si0 2 ) ; or may comprise another dielectric material such as Aluminium Oxide (Al 2 0 3 ) .
  • the sputterer includes a chamber which may be substantially filled with an inert gas such as
  • Argon preferably at a pressure of around 2mm of Hg, or a mixture of Argon and Oxygen, eg in the proportion 90%/l0%.
  • the Quantum Well Intermixing step may comprise Impurity-Free Vacancy Disordering (IFVD) .
  • IOVD Impurity-Free Vacancy Disordering
  • Quantum Well Intermixing (QWI) step also includes the subsequent step of annealing the device body portion including the dielectric layer at an elevated temperature .
  • the portion of the device body portion adjacent the dielectric cap may, for example, comprise a top or "capping" layer. It is believed that the damage arises due to breakage of bonds in the capping layer before annealing, eg the application of thermal energy by rapid thermal annealing, thereby expediting transfer of ion or atoms, eg Gallium Arsenide
  • the method may also include the step of defining a pattern in photoresist on a surface of the device body portion, depositing the dielectric layer and lifting off the photoresist so as to provide the dielectric layer on the said at least part of the surface of the device body portion.
  • the method may also include the step of depositing a further dielectric layer on the surface of the device body and on a surface of the dielectric layer prior to annealing, preferably by a technique other than sputtering, eg Plasma Enhanced Chemical Vapour Deposition (PECVD) .
  • PECVD Plasma Enhanced Chemical Vapour Deposition
  • the method may include the steps of depositing the further dielectric layer and then depositing the dielectric layer.
  • the dielectric layer may comprise an intermixing cap, the further dielectric layer may comprise an intermixing suppressing cap.
  • the thickness of the dielectric layer may be around 10 to a few hundred nm.
  • the annealing step may occur at a temperature of around 700°C to 1000°C for around 0.5 to 5 minutes, and preferably at substantially 800°C for around 1 minute.
  • Intermixing (QWI) step may include the step of: processing the device body portion so as to create extended defects at least in a portion of the device portion.
  • QWI Intermixing
  • Each extended defect may be understood to be a structural defect comprising a plurality of adjacent
  • said step of processing the device body portion comprises sputtering from the device body portion.
  • a magnetic field may be provided around the device body portion.
  • a magnetron sputterer may ' be used.
  • a (reverse) electrical bias may be applied across an electrode upon which the device body portion is provided so as to provide a "pre-etch” or cleansing of the device body portion.
  • the method may include the preceding step of depositing a dielectric layer on at least one other portion of the device body portion.
  • the dielectric layer may therefore act as a mask in defining the at least one portion.
  • the method may also include the step of depositing a further dielectric layer on the dielectric layer and/or on the at least one portion of the device body portion.
  • the dielectric layer and/or the further dielectric layer may be deposited by use of a magnetron sputterer.
  • the dielectric layer and/or the further dielectric layer may be deposited by a deposition technique other than by use of a diode sputterer, eg Plasma Enhanced Chemical Vapour Deposition
  • low damage dielectric layer (s) is/are provided which do not substantially affect an adjacent portion of the device body portion.
  • the dielectric layer (s) may beneficially substantially comprise silica (Si0 2 ) ; or may comprise another dielectric material such as Aluminium Oxide (A1 2 0 3 ) .
  • the sputterer includes a chamber which may be substantially filled with an inert gas such as Argon, preferably at • a pressure of around 2mm of Hg, or a mixture of Argon and Oxygen, eg in the proportion 90%/l0%.
  • the Quantum Well Intermixing (QWI) step may comprise Impurity-Free Vacancy Disordering (IFVD) .
  • the Quantum Well Intermixing (QWI) step also includes the subsequent step of annealing the device body portion including the dielectric layer at an elevated temperature .
  • the damage induced extended defects are introduced into the at least one portion of the device body portion; the at least one portion may, for example, comprise at least a part of a top or "capping" layer. It is believed that the damage arises due to breakage of bonds in the capping layer before annealing, eg the application of thermal energy by rapid thermal annealing, thereby inhibiting transfer of ion or atoms, eg Gallium Arsenide (GaAs) , from the at least one portion, eg into the further dielectric layer.
  • ion or atoms eg Gallium Arsenide (GaAs)
  • the method may comprise the step of: depositing the dielectric layer on a surface of the device body portion; defining a pattern in photoresist on a surface of the dielectric layer and lifting off at least part of the photoresist so as to provide the dielectric layer on said at least one other portion of the device body portion.
  • the method may also include the step of: depositing the further dielectric layer on a portion of the surface of the device body and on a surface of the dielectric layer prior to annealing.
  • the dielectric layer may comprise an intermixing cap, and the at least one portion of the device body portion and/or the further dielectric layer may comprise an intermixing suppressing cap.
  • the thickness of the dielectric layer (s) may be around 10 to a few hundred nm.
  • a subsequent annealing step may occur at a temperature of around 700°C to 1000°C for around 0.5 to 5 minutes, and in preferably at substantially 800°C for around 1 minute.
  • the step of passifying at least some dopants within at least a portion of the device body portion comprises placing the device body portion in a plasma of hydrogen or one of its isotopes or a mixture thereof.
  • the plasma of hydrogen which can be, for example, a capacitively or inductively coupled RF plasma, is at a pressure of around 0.1 mbar to 100 mbar, and preferably 1 mbar.
  • the device body portion is exposed to the plasma of hydrogen for around 10 min to 5 hr and preferably for around 2 hr .
  • exposing the device body portion to a hydrogen plasma causes hydrogen to diffuse or implant within the device body portion pairing or forming complexes with dopants and therefore passivating or neutralizing the electrical activity of dopants, such as p- or n-dopants. In this way optical losses within a region of the device body portion where the passified dopants are provided are reduced.
  • the region corresponds to a cladding layer of the optical device adjacent to a core layer including the Quantum Well (QW) structure, eg a p-doped cladding layer, as grown.
  • QW Quantum Well
  • a dielectric, eg Silica (Si0 2 ) , layer is deposited on at least part of the device body portion prior to step (b) and retained during step (b) .
  • the intermixing step may be carried out by one or more of : (i) diffusing a dopant, eg Silicon, Copper, Zinc or Sulphur; (ii) impurity free vacancy disordering; (iii) ion implementation, eg of an electrically active dopant or electrically inactive species ; (iv) exposure to plasma;
  • a method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure including the steps of:
  • an optical device fabricated from a method according to the first aspect of the present invention.
  • the optical device may be an integrated optical device or an optoelectronic device.
  • the device body portion may be fabricated in a III - V semiconductor materials system.
  • the III-V semiconductor materials system may be a Gallium Arsenide (GaAs) based system, and may therefore operate at a wavelength (s) of substantially between 600 and 1300nm.
  • the III - V semiconductor materials system may be an Indium Phosphide based system, and may therefore operate at a wavelength (s) of substantially between 1200 and 170 Onm.
  • the device body portion may be made at least partly from Aluminium Gallium Arsenide Arsenide (AlGaAs) , Indium Gallium Arsenide (InGaAs), Indium Gallium Arsenide Phosphide, (InGaAsP) , Indium Gallium Aluminium Arsenide (InGaAlAs) and/or Indium Gallium Aluminium Phosphide (InGaAlP) .
  • AlGaAs Aluminium Gallium Arsenide Arsenide
  • InGaAs Indium Gallium Arsenide
  • Indium Gallium Arsenide Phosphide Indium Gallium Arsenide Phosphide
  • InGaAlAs Indium Gallium Aluminium Arsenide
  • InGaAlP Indium Gallium Aluminium Phosphide
  • the device body portion may comprise a substrate, ie
  • GaAs or InP upon which are provided a first optical cladding layer, a core guiding layer, and a second optical cladding layer also optionally a low-resistance contact layer.
  • the Quantum Well (QW) -structure is provided within the core guiding layer.
  • the core guiding layer, as grown, may have a smaller band-gap and higher refractive index than the first and second optical cladding layers.
  • the passivated dopants may be within the second or the first or the first and second optical cladding layers.
  • the optical device may include one or more of : a passive waveguide, eg a. slab waveguide or a ridge waveguide or buried waveguide, a mode expander, mode compressor, or mode converter; a laser diode; an optical modulator; an optical amplifier; an optical switch, or the like.
  • a passive waveguide eg a. slab waveguide or a ridge waveguide or buried waveguide, a mode expander, mode compressor, or mode converter
  • a laser diode e.g. slab waveguide or a ridge waveguide or buried waveguide, a mode expander, mode compressor, or mode converter
  • a laser diode e.g. an optical modulator
  • an optical amplifier e.g. an optical amplifier
  • an optical switch e.g., a mode converter
  • the optical device may comprise an Extended Cavity Laser (ECL) .
  • ECL Extended Cavity Laser
  • the optical device may include a grating.
  • an optical device providing a device body portion including a Quantum Well (QW) structure as grown, wherein at least part of the Quantum Well (QW) structure is intermixed and at least some dopants within the device body portion are passivated.
  • QW Quantum Well
  • an optical integrated circuit, optoelectronic integrated circuit (OEIC) , or photonic integrated circuit (PIC) including at least one optical device according to either of the third or fourth aspects of the present invention.
  • OEIC optoelectronic integrated circuit
  • PIC photonic integrated circuit
  • a wafer of material including at least one device body portion when used in a method according to the first or second aspects of the present invention.
  • Figure 1 (a) - (q) a series of schematic views of processing steps involved in manufacture of an optical device according to a first embodiment of the present invention
  • Figure 2 a schematic view of a further processing step involved in manufacture of the optical device according to the first embodiment of the present invention
  • Figure 3 a series of schematic views of processing steps involved in manufacture of an optical device according to a second embodiment of the present invention
  • Figure 4 comparative photo- luminesence spectra of an as-grown sample and a sample processed using Quantum Well Intermixing (QWI) according to the present invention
  • Figure 5 comparative loss spectra of a sample without hydrogen passivation and a sample with hydrogen passivation according to the present invention
  • Figures 6 (a) & (b) graphs showing charge carrier distributions with depth of a MQW- based laser structure on InP without hydrogen passivation and with hydrogen passivation respectively, according to the present invention which results in a nearly complete neutralisation of p-dopants
  • Figure 7 graphs of optical output against current for a laser without hydrogen passivation and a laser with hydrogen passivation according to the present invention.
  • FIG. 1 (a) to (g) there is illustrated a series of schematic views of processing steps involved in a method of manufacturing an optical device, from a raw "sample” generally designated 5a, according to a first embodiment of the present invention.
  • the method begins by forming the sample 5a by starting with an n + substrate 10a which, in this embodiment, is made of Indium Phosphide (InP) .
  • n + substrate 10a which, in this embodiment, is made of Indium Phosphide (InP) .
  • Grown on the substrate 10a is a first n-type cladding layer 15a, a substantially intrinsic core guiding layer 20a, including at least one Quantum Well (QW) 25a, and a p-type second cladding layer 30a and beneficially a low-resistance contact layer.
  • the low-resistance contact layer 31a is beneficially provided in the case where the second cladding layer 30a is InP or close in composition thereto, so as to protect the second cladding layer 30a from the plasma used in the method hereinafter described.
  • the layers 15a, 20a, 30a are beneficially substantially lattice matched to the substrate 10a.
  • the layers 15a, 20a, 30a and the Quantum Well (QW) 25a are in this embodiment grown by Molecular Beam Epitaxy (MBE) . It should however be appreciated that other growth methods such as Metal Organic Chemical Vapour Deposition (MOCVD) can also be used.
  • MBE Molecular Beam Epitaxy
  • MOCVD Metal Organic Chemical Vapour Deposition
  • a layer of photoresist 35a on a surface of sample 5a is spun a layer of photoresist 35a, and a suitable mask is used to form a pattern on the photoresist by normal lithographic techniques such as lift-off as is shown in Figure 1(c) .
  • a layer of dielectric 40a such as Silica (Si0 2 ) is sputtered onto the sample 5a, for example by use of a diode sputterer.
  • the photoresist 35a is then washed off the sample 5a leaving a pattern of dielectric 40a, as is shown in Figure 1(e) .
  • the sample 5a is then annealed, for example at an elevated temperature of around 700°C to 1000°C for around 0.5 to 5 minutes, and in the preferred implementation at substantially 800°C for around 1 minute.
  • the annealing causes Gallium and Indium to diffuse into the sputtered dielectric layer 40a, and point defects and impurities to diffuse into the semiconductor. These impurities diffuse to the Quantum Well structure 25a thereby causing intermixing thereof.
  • An intermixed region 50a of the Quantum Well structure 25a is shown in Figure 1(g) .
  • the dielectric layers 40a and 45a are removed subsequent to annealing and intermixing.
  • the dielectric layers 40a and 45a may be washed off using hydrofluoric (HF) acid.
  • area region 50a of the Quantum Well structure 25a can be Quantum Well Intermixed (QWI) .
  • a ridge waveguide can be formed in the sample 5a by the following process steps.
  • a further dielectric layer 55a is deposited on the sample 5a.
  • a further layer of photoresist 60a is deposited on the further dielectric layer 55a.
  • a pattern is formed in the further photoresist layer 60a by normal photolithographic techniques .
  • a similar pattern is created in the further dielectric layer 55a in this embodiment by a reactive ion etching, eg with C 2 F 6 .
  • the photoresist is washed off as can be seen from Figure 1(1) , leaving the patterned further dielectric layer 55a.
  • a ridge 65a is formed in the sample 5a by reactive ion etching (RIE) , using CH 4 : H, .
  • the further dielectric layer 55a is removed, for example with hydrofluoric (HF) acid.
  • a yet further photoresist layer is spun on and patterned by photolithographic techniques on a surface of a sample 5a, as can be seen from Figure 1 (o) .
  • metalisation 75a is deposited on the surface of the sample 5a, so as to fabricate contacts on the sample 5a.
  • the yet further photoresist layer 70a is washed off by normal techniques, eg using acetone, so as to leave a portion of the metalisation 75a so as to form an electrical contact 80a to a portion of the sample 5a ( Figure 1 (q) .
  • a first portion 85a of the sample 5a, which includes the contact 80a therefore comprises an active device, while a second portion 90a of the sample 5a. comprises a passive waveguide section.
  • the contact 80a may also be annealed if desired.
  • Hydrogen is introduced into the chamber 100a at a pressure of around 1 m bar for around a time of 2 hr, while maintaining the sample at a temperature of around 220°C.
  • Hydrogen is diffused or implanted into the cladding layers 30a, 15a to interact with the p- and n-dopants dopants respectively therein, and thereby passivating dopants in the cladding layers 30a and 15a within the passive waveguide section 90a.
  • This step passivates at least some of the dopants within a portion of the two cladding layers 30a and 15a within the passive portion 90a of the device 5a, thereby reducing optical losses within the passive waveguide portion 90a.
  • a sample 5a can be fabricated into integrated optical device 115a providing active and passive device portions where the band-gap of the various portions is selectively tunable by Quantum Well Intermixing (QWI), while the passive portions exposed to H plasma provide low-loss interconnections between the active portions.
  • QWI Quantum Well Intermixing
  • FIG. 115b an integrated optical device, generally designated 115b, according to a second embodiment of the present invention.
  • the optical device .115b is made from a raw "sample” 5b, and is similar to the optical device formed by the sample 5a of the first embodiment herein before described, like parts being identified by like numerals but suffixed with 'bX
  • the optical device 5b it is noted includes two Quantum Well (QW) structures 25b, as- grown .
  • QW Quantum Well
  • the optical device 5b is formed from a method which varies from that of the first embodiment .
  • the ridge 65b is formed in the p-type upper cladding layer 30b.
  • the Quantum Wells (QWs) 25b are intermixed, for example, by an intermixing technique comprising depositing a dielectric, layer, or at least part of a surface of the device body portion so as to introduce structural defects at least into a portion of the device body portion adjacent the dielectric layer.
  • an intermixing technique comprising depositing a dielectric, layer, or at least part of a surface of the device body portion so as to introduce structural defects at least into a portion of the device body portion adjacent the dielectric layer.
  • a region 110b of the upper cladding layer 30b is passivated by hydrogen, ie p-dopants therein are passivated so as to reduce optical losses within the waveguide formed by the ridge 65b.
  • a completed device 115b is provided.
  • the upper and lower cladding layers 30b, 15b confine light in the vertical direction, and the ridge 65b formed by etching is used to provide lateral confinement.
  • the upper and lower cladding layers 30b, 15b are doped p-type and n-type respectively to allow carriers to be injected into the Quantum Wells (QWs) 25b to provide light emission, or to allow a reverse bias to be applied to the Quantum Wells (QWs) 25b so the device 115b can act as a modulator .
  • Quantum Wells (QWs) 25b are intermixed in the region of the ridge 65b, possibly to create a low-loss interconnecting waveguide. The location of the region containing the excess point defects and/or impurities required to induce QWI is illustrated. In this region, the band-gap of the Quantum Wells (QWs) 25b has been widened.
  • the dopants in the region in which light is guided have been passivated using hydrogen, so reducing FCA and IVBA in the guiding region.
  • Sample material used to fabricate waveguides was a laser structure with an emission waveguide of around 1.55 ⁇ m.
  • the active region was bounded by a stepped graded index (GRIN) waveguide core consisting of InGaAsP confining layers .
  • the structure which was lattice, matched to InP throughout, was completed by a 1.2 ⁇ m thick InP cladding layer and an InGaAs contact layer.
  • the first 0.2 ⁇ m of the upper cladding layer was an undoped spacer layer and the remaining 1.2 ⁇ m was doped with Zn to a concentration of 9 x 10 17 crrf 3 .
  • the lower cladding layer was Si doped to a concentration of 2 x 10 18 cm "3 .
  • the waveguide core was undoped, thus forming a pin structure with the intrinsic region restricted to the QWs and GRIN layers .
  • the sample used to fabricate the waveguides was firstly processed using QWI to blue- shift the absorption edge by around 90 nm (54 meV) , as shown in Figure 4.
  • Waveguides of 5 ⁇ m width were fabricated using routine photolithography and dry-etching. Then 200 nm Si0 2 was deposited on the sample to protect the sample during the subsequent hydrogen passivation process. Finally a window was opened on the top of the waveguide to allow the hydrogen atoms to diffuse into the sample through the window. Half of the sample was treated using hydrogen plasma. H passivation has been achieved by exposing the sample to Deuterium ( 2 H, isotope of H) in a capacitively coupled reactor for 2 hr at 200 °C using a RF plasma power density of around 0.1 W.cm "2 at a pressure of around 0.1 m bar
  • a passive waveguide was contained within a laser cavity, such as an Extended Cavity semiconductor Layer (ECL) .
  • ECL Extended Cavity semiconductor Layer
  • the purpose of the passive waveguide region within such a laser may be to reduce mode-locking repetition frequency, to reduce laser line- width or to contain elements designed to stabilize transverse or longitudinal modes of the laser.
  • the sample used for the fabrication of extended cavity lasers had an identical material structure to that described above in relation to Example 1. Again, the sample was processed using QWI so that the passive region in the sample (within which the passive section of the extended cavity laser was to be placed) exhibited a blue-shift in the absorption edge about 90 nm. The band-gap wavelength of the active region remained unchanged during QWI. Fabrication of the extended cavity lasers was essentially the same as for the waveguides described above, except that additional metal contacts were required on the sample so that current can be injected into the active region of the laser. The metal contact for the p-side was confined to only the active region of the sample. Metal contact annealing was performed at 360°C for 60 seconds using a rapid thermal annealer. The sample was cleaved into two smaller samples .
  • 500 ⁇ m all-active lasers and extended cavity lasers with active section of 500 ⁇ m and different lengths of passive section were cleaved from one of the samples.
  • the other sample was processed using H passivation, and again, was cleaved to form extended cavity lasers. All the devices were tested under pulsed conditions with the repetition rate of 1kHz and pulse with of 400 ns .
  • Figure 6 shows the light-current curves for the lasers without and with H passivation.
  • the 500,um all-active laser is also shown for comparison.
  • the threshold currents for the 500 ⁇ m/l000 ⁇ m and 500 ⁇ m/2000 ⁇ m ECLs were about 67 mA and 270 mA respectively before the H passivation.
  • the threshold currents were reduced dramatically to 50 mA for the same lengths respectively. Also the external quantum efficiencies were significantly increased after H processing.
  • the loss in the passive waveguides was estimated to lie in the range 8 to 14 cm “1 before hydrogen processing and was reduced to 3.4 to 3.9 cm “1 after hydrogen processing. This means a drop in losses in these devices by more than 20 and 40 dB/cm, respectively.
  • fabrication of ECLs necessitated a minimum of two different, if not three epitaxial growth sequences, and as many dry-etchings in-between to complete the whole device.
  • a whole device slice with constituent layers is realized in a single growth sequence and the ECLs are subsequently fabricated using successively the QWI processing, a dry-etch sequence for lateral confinement and finally the Hydrogen passivation.
  • yield of devices is enhanced since the number of highly risky growth and dry-etch sequences are considerably reduced. This also means that at a low cost and high yield, devices with equivalent, if not with better performance, can be fabricated in a very- simple way.
  • the coupling loss between a waveguide and a single mode fiber is very high, typically around lOdB, and the position tolerance for efficient coupling is extremely critical .
  • Using a waveguide mode converter can reduce the coupling loss to less than IdB, depending on the wafer structure design. Furthermore, the tight alignment tolerances are relaxed.
  • the embodiments of the present invention provide an advantageous combination of Quantum Well Intermixing (QWI) with passivation of (p-) dopants using hydrogen (or one of its isotypes) , to reduce the absorption of light in a PIC.
  • QWI Quantum Well Intermixing
  • p- dopants using hydrogen
  • the present invention considerably lightens the device manufacturing technology by reducing the number of processing steps.
  • the invention includes the case where the combination of QWI and hydrogenation is used to form low loss waveguides for use as optical interconnects within a PIC.
  • the combination of QWI and dopant passivation are used to reduce loss in ' a passive waveguide region in which a cross-section of an optical mode is expanded or compressed in area; light in a passive waveguide is confined in one dimension (slab waveguide) or in two dimensions; a passive waveguide contains a grating- structure, the grating being either a one-dimensional, two- dimensional or three-dimensional structure; the coupling between the grating and the optical field being weak or strong (so-called photonic band-gap structure); the waveguide core, or one or both of the waveguide cladding layers, are composed of multiple Quantum Wells (QWs) or closely multiple Quantum Well (QW) structures known as superlattices ; the multiple Quantum Well (QW) layers optionally being disordere
  • QWs Quantum Wells
  • QW Quantum Well

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Abstract

There is disclosed an improved method of manufacturing optical devices (115a; 115b). A requirement for photonic Integrated Circuits is the realization of low-loss optical waveguides. Optical absorption by Fundamental Edge Absorption (FEA) can be reduced by using Quantum Well Intermixing (QWI) to widen the band-gap of passive waveguides. However, impurities and/or and structural defects responsible for (QWI) are all usually charged and have free electrons or holes associated with them, giving rise to optical absorption by Free-Carrier Absorption (FCA). Accordingly, the invention provides a method of manufacturing an optical device (115a; 115b), a device body portion (5a; 5b) from which the device (115a; l15b) is to be made including a Quantum Well (QW) structure (25a; 25b). )the method including the steps of: intermixing at least part of the Quantum well (QW) structure (25a; 25b); and passivating at least some dopants and/or point defects within at least a portion of the device body portion (5a; 5b). By 'passivating' is meant neutralizing the electronic activity of the dopants.

Description

IMPROVEMENTS IN AND RELATING TO OPTOELECTRONIC DEVICES
FIELD OF INVENTION
This invention relates to a method of manufacturing optical devices, and in particular, though not exclusively, to manuf cturing of integrated optical devices, optoelectronic devices or photonic devices, for example, semiconductor optoelectronic devices such as laser diodes, optical modulators, optical amplifiers, optical switches, passive waveguide devices such as mode expanders, compressors and converters, and the like. The invention further relates to devices made by such a method, as well as to Optoelectronic Integrated Circuits (OEICs) , and Photonic Integrated Circuits (PICs) , including such a device or devices.
BACKGROUND TO INVENTION
Monolithic integration of semiconductor optical devices is concerned, with implementation of several optical functions, such as generation, modulation, switching and detection of light onto one substrate. Such monolithic circuits are known as Photonic Integrated Circuits (PICs) , and offer considerable performance and functionality advantages over discrete devices. They also offer reduced packaging and manufacturing costs. A fundamental requirement for PICs is the realisation of low-loss optical waveguides to link different components to form a functional circuit.
In a practical PIC, the semiconductor materials forming an optical -waveguide absorb -light through three principal mechanisms . The first is fundamental edge absorption (FEA) due to a carrier being excited across the band-gap by absorbing a photon (band-to-band absorption) . The second loss mechanism is free-carrier absorption (FCA) , due to electrons and holes moving in response to the electric field of the light wave ' and losing energy through scattering collisions. The third mechanism referred to as inter-valence band absorption (IVBA) , is associated with the presence of free hole transitions among- the heavy-hole and spin-orbit split-off bands, and is directly proportional to a concentration of holes in the valence band giving rise to an absorption coefficient at least 7 to 8 times larger than that of FCA. At an optical wavelength corresponding to the band- gap of the semiconductor, FEA is the strongest absorption mechanism.
Quantum Well Intermixing (QWI) is a post-growth technique that can be used to modify selectively the profile of a Quantum Well (QW) , leading to a "blue-shift" (ie a shift towards shorter wavelengths) of the optical absorption edge. FEA can thus be reduced to a minimum by using QWI to widen the band-gap of passive waveguides.
There is a variety of Quantum Well Intermixing techniques . Some of these involve the diffusion of an electrically active impurity into the semiconductor, which may be either a donor or an acceptor. One mechanism by which the impurity can induce intermixing is by the so-called "Fermi-level" effect. Since the presence of the dopant species influences the position of the Fermi- level, there is a resulting change in the concentrations of charged point defects in the semiconductor. This happens partly because the point defects in semiconductors are charged and themselves behave as donors or acceptors . The diffusion of the point defects - particularly lattice vacancies, but also interstitials providing there is some exchange between lattice atoms and interstitials - is then responsible for QWI. In addition, some impurity species, (eg zinc in GaAs) diffuse as interstitials hop into and out of lattice sites (the so-called 'kick-out' mechanism) . This process can result in QWI. Finally there are "impurity free" QWI processes, in which the point defects are generated by other means . These techniques include illumination by CW or pulsed lasers, or annealing samples with a suitable dielectric cap on the surface in which lattice matrix elements can dissolve so generating vacancies . In all cases the point defects behave as donors or acceptors .
QWI arises from the diffusion of point, defects or from impurities. In general the point defects are charged and have free electrons or holes associated with them. Impurities and/or structural defects responsible for QWI are also usually charged and have free electrons or holes associated with them. There is therefore a "need to lower the concentration of free carriers as these give rise to optical absorption via the other two mechanisms . FCA is proportional to the concentrations of free electrons and holes in the semiconductor layers; therefore to reduce FCA in thermal equilibrium the concentration of the majority carrier (electrons in n- type material, holes in p-type) should be lowered. IVBA depends only on the hole concentration so the contribution thereof to the total optical propagation loss is reduced by lowering the hole concentration.
Furthermore, in conventional laser structures such as double heterostructures (DH) , separate confinement heterostructures (SCH) or graded index separate confinement heterostructures (GRINSCH) , the optical overlap with the waveguide core is around 50%. Generally around 25% of the optical field extends into a p-doped waveguide cladding layer, in which the hole concentration typically lies in the range lxl016crrf3 to lxl019crrf3. As a result of the overlap of the optical field with the p- type upper cladding layer, FCA and IVBA make contributions to the optical propagation loss. The magnitude of the loss depends strongly on material composition and the optical wavelength. Experiment shows absorption coefficients of about 13cm"1 at 1.3μm and 25cm"1 at 1.6μm for In0 53Ga047As , InP, and GaAs crystals for a hole concentration of 1018cm"3.
It is an object of at least one aspect of the present invention to provide an improved method of manufacturing an optical device having reduced optical losses as compared to the prior art .
It is a further object of at least one aspect of the present invention to provide a simpler and easier to implement method of manufacturing an optical device requiring fewer processing steps than in the prior art .
SUMMARY OF INVENTION
According to a first aspect of the present invention there is provided a method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure, the method including the steps of :
(a) intermixing at least part of the Quantum Well (QW) structure;
(b) passivating at least some dopants and/or point defects within at least a portion of the device body portion.
Herein by "passivating" or "passifying" is meant neutralising the electronic activity of the dopants and/or point defects .
The dopants may preferably be p-dopants, but may instead be n-dopants or indeed may be both p- and n- dopants . Step (a) is most preferably undertaken before step
(b) , however in a variant step (b) may be undertaken before step (a) .
The step of intermixing at least part of the Quantum Well (QW) - Quantum Well Intermixing (QWI) - may result in any effective increase in band-gap of a region of the device body portion providing the Quantum Well (QW) structure .
The step of passivating at least dopants within the device body position may act to reduce optical absorption within the device, particularly absorption via IVBA. Preferably the method of manufacture also includes the preceding steps of : providing a substrate; growing on the substrate : a first optical cladding layer; a core guiding layer including the Quantum Well
(QW) structure; and a second optical cladding layer. The method may also comprise the step of growing on the second optical cladding layer a contact layer. The contact layer may, in use, serve to protect the second optical cladding layer, eg from Hydrogen (H) or Deuterium (D) .
The first optical cladding layer, core guiding layer, and second optical cladding layer and optional top contact layer may preferably be grown by Molecular Beam
Epitaxy (MBE) or Metal Organic Chemical Vapour Deposition (MOCVD) or indeed by any other suitable growth technique.
In one form of the invention the Quantum Well Intermixing (QWI) step may include the step of: depositing a dielectric layer on at least part of a surface of the device body portion so as to introduce structural defects at least into a portion of the device body portion adjacent the dielectric layer. Such a method step is disclosed in GB 01 01 635.1 of 23 January 2001 (published as GB 2 373 148A on 11 August 2002) also by one of the present Applicants, the content of which is incorporated herein by reference .
The structural defects may include "point" defects. Preferably, and advantageously, the dielectric layer is deposited by sputtering. In a preferred embodiment the dielectric layer is deposited by sputtering using a diode sputterer.
The dielectric layer may beneficially substantially comprise silica (Si02) ; or may comprise another dielectric material such as Aluminium Oxide (Al203) .
Preferably, the sputterer includes a chamber which may be substantially filled with an inert gas such as
Argon, preferably at a pressure of around 2mm of Hg, or a mixture of Argon and Oxygen, eg in the proportion 90%/l0%.
The Quantum Well Intermixing step may comprise Impurity-Free Vacancy Disordering (IFVD) .
Preferably, in this form of the invention the
Quantum Well Intermixing (QWI) step also includes the subsequent step of annealing the device body portion including the dielectric layer at an elevated temperature .
It has been surprisingly found that by depositing the dielectric layer used in QWI techniques such as IFVD by sputtering, damage induced point defects are introduced into the portion of the device body portion adjacent the dielectric cap; the portion may, for example, comprise a top or "capping" layer. It is believed that the damage arises due to breakage of bonds in the capping layer before annealing, eg the application of thermal energy by rapid thermal annealing, thereby expediting transfer of ion or atoms, eg Gallium Arsenide
(GaAs) , from the capping layer into the dielectric layer.
In a first embodiment of this form of the invention the method may also include the step of defining a pattern in photoresist on a surface of the device body portion, depositing the dielectric layer and lifting off the photoresist so as to provide the dielectric layer on the said at least part of the surface of the device body portion.
In said first embodiment of this form of the invention, the method may also include the step of depositing a further dielectric layer on the surface of the device body and on a surface of the dielectric layer prior to annealing, preferably by a technique other than sputtering, eg Plasma Enhanced Chemical Vapour Deposition (PECVD) .
In a second embodiment of this form of the invention the method may include the steps of depositing the further dielectric layer and then depositing the dielectric layer.
In said first and second embodiments of this form, the dielectric layer may comprise an intermixing cap, the further dielectric layer may comprise an intermixing suppressing cap. The thickness of the dielectric layer may be around 10 to a few hundred nm.
The annealing step may occur at a temperature of around 700°C to 1000°C for around 0.5 to 5 minutes, and preferably at substantially 800°C for around 1 minute. In another form of the invention the Quantum Well
Intermixing (QWI) step may include the step of: processing the device body portion so as to create extended defects at least in a portion of the device portion. Such a method step is disclosed in GB 01 02 536.0 of
1 February 2001 (published as GB 2 371 919A on 7 August
2002) also by one of the present Applicants, the content of which is incorporated herein by reference.
Each extended defect may be understood to be a structural defect comprising a plurality of adjacent
"point" defects.
Preferably said step of processing the device body portion comprises sputtering from the device body portion. In said step of sputtering from the device body portion a magnetic field may be provided around the device body portion. In said step of sputtering from the device body portion a magnetron sputterer may' be used.
In said step of sputtering from the device body portion a (reverse) electrical bias may be applied across an electrode upon which the device body portion is provided so as to provide a "pre-etch" or cleansing of the device body portion.
In a preferred implementation the method may include the preceding step of depositing a dielectric layer on at least one other portion of the device body portion.
The dielectric layer may therefore act as a mask in defining the at least one portion.
The method may also include the step of depositing a further dielectric layer on the dielectric layer and/or on the at least one portion of the device body portion.
Advantageously the dielectric layer and/or the further dielectric layer may be deposited by use of a magnetron sputterer. Alternatively, the dielectric layer and/or the further dielectric layer may be deposited by a deposition technique other than by use of a diode sputterer, eg Plasma Enhanced Chemical Vapour Deposition
(PECVD) . By either of these deposition techniques low damage dielectric layer (s) is/are provided which do not substantially affect an adjacent portion of the device body portion.
The dielectric layer (s) may beneficially substantially comprise silica (Si02) ; or may comprise another dielectric material such as Aluminium Oxide (A1203) . Preferably, the sputterer includes a chamber which may be substantially filled with an inert gas such as Argon, preferably at • a pressure of around 2mm of Hg, or a mixture of Argon and Oxygen, eg in the proportion 90%/l0%. The Quantum Well Intermixing (QWI) step may comprise Impurity-Free Vacancy Disordering (IFVD) . Preferably, in this another form of the invention the Quantum Well Intermixing (QWI) step also includes the subsequent step of annealing the device body portion including the dielectric layer at an elevated temperature .
It has been surprisingly found that by sputtering from the device body portion as a step in a QWI technique' such as IFVD, preferably by use of a magnetron sputterer, damage induced extended defects are introduced into the at least one portion of the device body portion; the at least one portion may, for example, comprise at least a part of a top or "capping" layer. It is believed that the damage arises due to breakage of bonds in the capping layer before annealing, eg the application of thermal energy by rapid thermal annealing, thereby inhibiting transfer of ion or atoms, eg Gallium Arsenide (GaAs) , from the at least one portion, eg into the further dielectric layer.
In a preferred embodiment of this another form of the invention the method may comprise the step of: depositing the dielectric layer on a surface of the device body portion; defining a pattern in photoresist on a surface of the dielectric layer and lifting off at least part of the photoresist so as to provide the dielectric layer on said at least one other portion of the device body portion.
In said preferred embodiment of this another form of the invention, the method may also include the step of: depositing the further dielectric layer on a portion of the surface of the device body and on a surface of the dielectric layer prior to annealing.
In said preferred embodiment of this another form of the invention, the dielectric layer may comprise an intermixing cap, and the at least one portion of the device body portion and/or the further dielectric layer may comprise an intermixing suppressing cap. The thickness of the dielectric layer (s) may be around 10 to a few hundred nm.
A subsequent annealing step may occur at a temperature of around 700°C to 1000°C for around 0.5 to 5 minutes, and in preferably at substantially 800°C for around 1 minute.
In a most preferred form of the invention the step of passifying at least some dopants within at least a portion of the device body portion comprises placing the device body portion in a plasma of hydrogen or one of its isotopes or a mixture thereof.
Preferably the plasma of hydrogen which can be, for example, a capacitively or inductively coupled RF plasma, is at a pressure of around 0.1 mbar to 100 mbar, and preferably 1 mbar. Preferably also the device body portion is exposed to the plasma of hydrogen for around 10 min to 5 hr and preferably for around 2 hr .
It is believed that exposing the device body portion to a hydrogen plasma causes hydrogen to diffuse or implant within the device body portion pairing or forming complexes with dopants and therefore passivating or neutralizing the electrical activity of dopants, such as p- or n-dopants. In this way optical losses within a region of the device body portion where the passified dopants are provided are reduced.
Preferably the region corresponds to a cladding layer of the optical device adjacent to a core layer including the Quantum Well (QW) structure, eg a p-doped cladding layer, as grown.
In an advantageous embodiment a dielectric, eg Silica (Si02) , layer is deposited on at least part of the device body portion prior to step (b) and retained during step (b) . The intermixing step may be carried out by one or more of : (i) diffusing a dopant, eg Silicon, Copper, Zinc or Sulphur; (ii) impurity free vacancy disordering; (iii) ion implementation, eg of an electrically active dopant or electrically inactive species ; (iv) exposure to plasma;
(v) laser melting or laser irradiation intermixing; (vi) intermixing by diffusion of structural point defects such as from an epitaxial layer. According to a second aspect of the present invention there is provided a method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure, the method including the steps of:
(a) intermixing at least part of the Quantum Well (QW) structure;
(b) removing free carriers, eg by passivating dopants and/or point defects, within at least a portion of the device body portion.
According to a third aspect of the present invention there is provided an optical device fabricated from a method according to the first aspect of the present invention.
The optical device may be an integrated optical device or an optoelectronic device.
The device body portion may be fabricated in a III - V semiconductor materials system.
In one embodiment- the III-V semiconductor materials system may be a Gallium Arsenide (GaAs) based system, and may therefore operate at a wavelength (s) of substantially between 600 and 1300nm. Alternatively, in a further embodiment the III - V semiconductor materials system may be an Indium Phosphide based system, and may therefore operate at a wavelength (s) of substantially between 1200 and 170 Onm. The device body portion may be made at least partly from Aluminium Gallium Arsenide Arsenide (AlGaAs) , Indium Gallium Arsenide (InGaAs), Indium Gallium Arsenide Phosphide, (InGaAsP) , Indium Gallium Aluminium Arsenide (InGaAlAs) and/or Indium Gallium Aluminium Phosphide (InGaAlP) .
The device body portion may comprise a substrate, ie
GaAs or InP, upon which are provided a first optical cladding layer, a core guiding layer, and a second optical cladding layer also optionally a low-resistance contact layer.
Preferably the Quantum Well (QW) -structure is provided within the core guiding layer. The core guiding layer, as grown, may have a smaller band-gap and higher refractive index than the first and second optical cladding layers.
The passivated dopants may be within the second or the first or the first and second optical cladding layers.
The optical device may include one or more of : a passive waveguide, eg a. slab waveguide or a ridge waveguide or buried waveguide, a mode expander, mode compressor, or mode converter; a laser diode; an optical modulator; an optical amplifier; an optical switch, or the like. Particularly the optical device may comprise an Extended Cavity Laser (ECL) . The optical device may include a grating.
According to a fourth aspect of the present invention there is provided an optical device providing a device body portion including a Quantum Well (QW) structure as grown, wherein at least part of the Quantum Well (QW) structure is intermixed and at least some dopants within the device body portion are passivated. According to a fifth aspect of the present invention, there is provided an optical integrated circuit, optoelectronic integrated circuit (OEIC) , or photonic integrated circuit (PIC) including at least one optical device according to either of the third or fourth aspects of the present invention. According to a sixth aspect of the present invention, there is provided a device body portion ("sample") when used in a method according to the first or second aspects of the present invention.
According to a seventh aspect of the present invention, there is provided a wafer of material including at least one device body portion when used in a method according to the first or second aspects of the present invention.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings, which are:
Figure 1 (a) - (q) a series of schematic views of processing steps involved in manufacture of an optical device according to a first embodiment of the present invention;
Figure 2 a schematic view of a further processing step involved in manufacture of the optical device according to the first embodiment of the present invention;
Figure 3 a series of schematic views of processing steps involved in manufacture of an optical device according to a second embodiment of the present invention; Figure 4 comparative photo- luminesence spectra of an as-grown sample and a sample processed using Quantum Well Intermixing (QWI) according to the present invention;
Figure 5 comparative loss spectra of a sample without hydrogen passivation and a sample with hydrogen passivation according to the present invention; Figures 6 (a) & (b) graphs showing charge carrier distributions with depth of a MQW- based laser structure on InP without hydrogen passivation and with hydrogen passivation respectively, according to the present invention which results in a nearly complete neutralisation of p-dopants; and Figure 7 graphs of optical output against current for a laser without hydrogen passivation and a laser with hydrogen passivation according to the present invention.
DETAILED DESCRIPTION OF DRAWINGS
Referring initially to Figures 1 (a) to (g) , there is illustrated a series of schematic views of processing steps involved in a method of manufacturing an optical device, from a raw "sample" generally designated 5a, according to a first embodiment of the present invention.
The method begins by forming the sample 5a by starting with an n+ substrate 10a which, in this embodiment, is made of Indium Phosphide (InP) . Grown on the substrate 10a is a first n-type cladding layer 15a, a substantially intrinsic core guiding layer 20a, including at least one Quantum Well (QW) 25a, and a p-type second cladding layer 30a and beneficially a low-resistance contact layer. The low-resistance contact layer 31a is beneficially provided in the case where the second cladding layer 30a is InP or close in composition thereto, so as to protect the second cladding layer 30a from the plasma used in the method hereinafter described. The layers 15a, 20a, 30a are beneficially substantially lattice matched to the substrate 10a. The layers 15a, 20a, 30a and the Quantum Well (QW) 25a are in this embodiment grown by Molecular Beam Epitaxy (MBE) . It should however be appreciated that other growth methods such as Metal Organic Chemical Vapour Deposition (MOCVD) can also be used.
Referring to Figure 1 (b) on a surface of sample 5a is spun a layer of photoresist 35a, and a suitable mask is used to form a pattern on the photoresist by normal lithographic techniques such as lift-off as is shown in Figure 1(c) . As is shown in Figure 1(d) a layer of dielectric 40a such as Silica (Si02) is sputtered onto the sample 5a, for example by use of a diode sputterer. The photoresist 35a is then washed off the sample 5a leaving a pattern of dielectric 40a, as is shown in Figure 1(e) .
As is shown in Figure 1(f), a further dielectric layer
45, for example Silica (Si02) , is deposited by a second
(different) deposition technique such as Plasma Enhanced Chemical Vapour Deposition (PECVD) . The sample 5a is then annealed, for example at an elevated temperature of around 700°C to 1000°C for around 0.5 to 5 minutes, and in the preferred implementation at substantially 800°C for around 1 minute. The annealing causes Gallium and Indium to diffuse into the sputtered dielectric layer 40a, and point defects and impurities to diffuse into the semiconductor. These impurities diffuse to the Quantum Well structure 25a thereby causing intermixing thereof. An intermixed region 50a of the Quantum Well structure 25a is shown in Figure 1(g) . As can also be seen from Figure 1 (g) , the dielectric layers 40a and 45a are removed subsequent to annealing and intermixing. For example, the dielectric layers 40a and 45a .may be washed off using hydrofluoric (HF) acid.
Thus as shown in Figures 1(a) to 1(g) area region 50a of the Quantum Well structure 25a can be Quantum Well Intermixed (QWI) .
Referring now to Figures 1 (h) to 1 (n) , a ridge waveguide can be formed in the sample 5a by the following process steps. Referring to Figure 1(h) , a further dielectric layer 55a is deposited on the sample 5a. Next, as shown in Figure l(i), a further layer of photoresist 60a is deposited on the further dielectric layer 55a. Next, as can be seen from Figure l(j) , a pattern is formed in the further photoresist layer 60a by normal photolithographic techniques . Subsequently, as shown in Figure 1 (k) , a similar pattern is created in the further dielectric layer 55a in this embodiment by a reactive ion etching, eg with C2F6. The photoresist is washed off as can be seen from Figure 1(1) , leaving the patterned further dielectric layer 55a. Referring to Figure 1 (m) , a ridge 65a is formed in the sample 5a by reactive ion etching (RIE) , using CH4 : H, . As can be seen from Figure 1 (n) , the further dielectric layer 55a is removed, for example with hydrofluoric (HF) acid. A yet further photoresist layer is spun on and patterned by photolithographic techniques on a surface of a sample 5a, as can be seen from Figure 1 (o) . Referring to Figure 1 (p) , metalisation 75a is deposited on the surface of the sample 5a, so as to fabricate contacts on the sample 5a. Next, the yet further photoresist layer 70a is washed off by normal techniques, eg using acetone, so as to leave a portion of the metalisation 75a so as to form an electrical contact 80a to a portion of the sample 5a (Figure 1 (q) . A first portion 85a of the sample 5a, which includes the contact 80a therefore comprises an active device, while a second portion 90a of the sample 5a. comprises a passive waveguide section. The contact 80a may also be annealed if desired.
Referring now to Figure 2, subsequent to the processing steps of Figures 1 (a) to 1 (q) , dopants within a portion of the cladding layers 30a and 15a within the Quantum Well Intermixed portion 90a of the sample 5a, are passified by the following technique. The sample 5a is placed on a heatable sample holder (platen) 95a comprising a first capactive plate within a chamber 100a. In chamber 100a, the RF plasma is established between the first capacitance plate 95a and a second capacitance plate 105a. It should however be appreciated that other plasma techniques such as dc, inductively coupled RF or microwave plasmas can also be employed. Hydrogen is introduced into the chamber 100a at a pressure of around 1 m bar for around a time of 2 hr, while maintaining the sample at a temperature of around 220°C. By this process Hydrogen is diffused or implanted into the cladding layers 30a, 15a to interact with the p- and n-dopants dopants respectively therein, and thereby passivating dopants in the cladding layers 30a and 15a within the passive waveguide section 90a. This step passivates at least some of the dopants within a portion of the two cladding layers 30a and 15a within the passive portion 90a of the device 5a, thereby reducing optical losses within the passive waveguide portion 90a.
Further charged point defects in the cladding layers 30a, 15a as well as within the waveguide core 20a, including the intermixed QW 25a are passivated. By the processing steps shown in Figures 1(a) to 1 (q) and in Figure 2, a sample 5a can be fabricated into integrated optical device 115a providing active and passive device portions where the band-gap of the various portions is selectively tunable by Quantum Well Intermixing (QWI), while the passive portions exposed to H plasma provide low-loss interconnections between the active portions.
Referring now to Figures 3 (a) to 3 (d) , there is shown an integrated optical device, generally designated 115b, according to a second embodiment of the present invention. The optical device .115b is made from a raw "sample" 5b, and is similar to the optical device formed by the sample 5a of the first embodiment herein before described, like parts being identified by like numerals but suffixed with 'bX The optical device 5b, it is noted includes two Quantum Well (QW) structures 25b, as- grown .
The optical device 5b is formed from a method which varies from that of the first embodiment . As can be seen from Figures 3a, (b) , (c) and (d) in the second embodiment, the ridge 65b is formed in the p-type upper cladding layer 30b. Next, as can be seen from Figure 3 (b) , the Quantum Wells (QWs) 25b are intermixed, for example, by an intermixing technique comprising depositing a dielectric, layer, or at least part of a surface of the device body portion so as to introduce structural defects at least into a portion of the device body portion adjacent the dielectric layer.- Such a method is disclosed in GB 01 01 635.1 of 23 January 2001 (published as GB 2 372 148 A on 14 August 2002), also by one of the present Applicants, the content of which is incorporated herein by reference. Alternatively, the Quantum Well Intermixing (QWI) process may include processing the device body portion so as to create extended defects at least in a portion of the device body portion. Such a method is disclosed in GB 01 02 536.0 of
1 February 2001 (published as GB 2 371 919 A on 7 August
2002) , also by one of the present Applicants, the content of which is incorporated herein by reference.
Next, as can be seen from Figure 3(c) , a region 110b of the upper cladding layer 30b, is passivated by hydrogen, ie p-dopants therein are passivated so as to reduce optical losses within the waveguide formed by the ridge 65b. By these method steps a completed device 115b is provided.
In the ridge waveguide structure of Figures 3 (a) to (d) , the upper and lower cladding layers 30b, 15b confine light in the vertical direction, and the ridge 65b formed by etching is used to provide lateral confinement. ' The upper and lower cladding layers 30b, 15b are doped p-type and n-type respectively to allow carriers to be injected into the Quantum Wells (QWs) 25b to provide light emission, or to allow a reverse bias to be applied to the Quantum Wells (QWs) 25b so the device 115b can act as a modulator .
The Quantum Wells (QWs) 25b are intermixed in the region of the ridge 65b, possibly to create a low-loss interconnecting waveguide. The location of the region containing the excess point defects and/or impurities required to induce QWI is illustrated. In this region, the band-gap of the Quantum Wells (QWs) 25b has been widened.
The dopants in the region in which light is guided have been passivated using hydrogen, so reducing FCA and IVBA in the guiding region.
EXPERIMENTAL EXAMPLE 1
A first experimental example will now be given. Sample material used to fabricate waveguides was a laser structure with an emission waveguide of around 1.55 μm. The material was grown on a (100 ) -oriented n-type InP substrate with an active region consisting of five 65 A InGaAs wells with 120 A InGaAsP (λg = 1.26 μm, whereλg is the wavelength corresponding to the band-gap) barriers. The active region was bounded by a stepped graded index (GRIN) waveguide core consisting of InGaAsP confining layers . The thicknesses and compositions of these layers (from the QWs outward) were 500 A of InGaAsP with λg =
1.18 μm and 800 A of λg = 1.08 μm . The structure, which was lattice, matched to InP throughout, was completed by a 1.2 μm thick InP cladding layer and an InGaAs contact layer. The first 0.2 μm of the upper cladding layer was an undoped spacer layer and the remaining 1.2 μm was doped with Zn to a concentration of 9 x 1017crrf3. The lower cladding layer was Si doped to a concentration of 2 x 1018cm"3. The waveguide core was undoped, thus forming a pin structure with the intrinsic region restricted to the QWs and GRIN layers .
The sample used to fabricate the waveguides was firstly processed using QWI to blue- shift the absorption edge by around 90 nm (54 meV) , as shown in Figure 4.
Waveguides of 5 μm width were fabricated using routine photolithography and dry-etching. Then 200 nm Si02 was deposited on the sample to protect the sample during the subsequent hydrogen passivation process. Finally a window was opened on the top of the waveguide to allow the hydrogen atoms to diffuse into the sample through the window. Half of the sample was treated using hydrogen plasma. H passivation has been achieved by exposing the sample to Deuterium (2H, isotope of H) in a capacitively coupled reactor for 2 hr at 200 °C using a RF plasma power density of around 0.1 W.cm"2 at a pressure of around 0.1 m bar
Optical transmission measurements were performed on waveguides with and without subjection to the hydrogen passivation process. Experiment shows a loss reduction of around 10 -dB cm"1 (2.4 cm "11 at the wavelength of 1.55 μ . Figure 5 shows measured waveguide loss spectra for waveguides with and without hydrogen passivation process. Figure 6 shows measured charge carrier distributions across the p-i-n structure before and after the hydrogen passivation process revealing a nearly complete neutralization of acceptors in the p-doped upper cladding layer. As can be seen from Figure 6, in the example InP based sample only the p-dopants are observed as being passivated. It has also been observed in example GaAs based samples that both p- and n-dopants have been passivated.
EXPERIMENTAL EXAMPLE 2
A second experimental example will now be given. In this example a passive waveguide was contained within a laser cavity, such as an Extended Cavity semiconductor Layer (ECL) . The purpose of the passive waveguide region within such a laser may be to reduce mode-locking repetition frequency, to reduce laser line- width or to contain elements designed to stabilize transverse or longitudinal modes of the laser. In such lasers it is important to minimize propagation loss in the passive waveguide; optical propagation loss within a laser cavity will raise the threshold current at which lasing occurs, and if the propagation loss is excessively high, the laser will not function at all. As an example, we used the combination of QWI and spatially localized H passivation in the QWI processed region to reduce the threshold current of an integrated extended cavity ridge waveguide laser. The sample used for the fabrication of extended cavity lasers had an identical material structure to that described above in relation to Example 1. Again, the sample was processed using QWI so that the passive region in the sample (within which the passive section of the extended cavity laser was to be placed) exhibited a blue-shift in the absorption edge about 90 nm. The band-gap wavelength of the active region remained unchanged during QWI. Fabrication of the extended cavity lasers was essentially the same as for the waveguides described above, except that additional metal contacts were required on the sample so that current can be injected into the active region of the laser. The metal contact for the p-side was confined to only the active region of the sample. Metal contact annealing was performed at 360°C for 60 seconds using a rapid thermal annealer. The sample was cleaved into two smaller samples .
500μm all-active lasers and extended cavity lasers with active section of 500 μm and different lengths of passive section were cleaved from one of the samples. The other sample was processed using H passivation, and again, was cleaved to form extended cavity lasers. All the devices were tested under pulsed conditions with the repetition rate of 1kHz and pulse with of 400 ns . Figure 6 shows the light-current curves for the lasers without and with H passivation. The 500,um all-active laser is also shown for comparison. As can be seen, the threshold currents for the 500μm/l000μm and 500μm/2000μm ECLs were about 67 mA and 270 mA respectively before the H passivation. After the H process treatment, the threshold currents were reduced dramatically to 50 mA for the same lengths respectively. Also the external quantum efficiencies were significantly increased after H processing. The loss in the passive waveguides was estimated to lie in the range 8 to 14 cm"1 before hydrogen processing and was reduced to 3.4 to 3.9 cm"1 after hydrogen processing. This means a drop in losses in these devices by more than 20 and 40 dB/cm, respectively. In the prior art fabrication of ECLs necessitated a minimum of two different, if not three epitaxial growth sequences, and as many dry-etchings in-between to complete the whole device. In contrast, in the present invention a whole device slice with constituent layers is realized in a single growth sequence and the ECLs are subsequently fabricated using successively the QWI processing, a dry-etch sequence for lateral confinement and finally the Hydrogen passivation. In other words, in the invention, yield of devices is enhanced since the number of highly risky growth and dry-etch sequences are considerably reduced. This also means that at a low cost and high yield, devices with equivalent, if not with better performance, can be fabricated in a very- simple way.
EXPERIMENTAL EXAMPLE 3
A third experimental sample will now be given. In this example the combination of QWI and passivation was used to reduce the loss in a passive waveguide region in which the cross-section of the optical mode is expanded or compressed in area.
Usually the coupling loss between a waveguide and a single mode fiber is very high, typically around lOdB, and the position tolerance for efficient coupling is extremely critical . Using a waveguide mode converter can reduce the coupling loss to less than IdB, depending on the wafer structure design. Furthermore, the tight alignment tolerances are relaxed. We have grown a structure in which a layer of phosphide quaternary (InGaAsP) with thickness of 5μm is inserted between the waveguide layer and lower cladding layer of the normal laser structure described above. Coupling loss as low as 1.8dB are expected.
It will be appreciated that the embodiments of the present invention hereinbefore described are given by way of example only, and are not meant to limit the scope thereof in any way.
It will particularly be appreciated that the embodiments of the present invention provide an advantageous combination of Quantum Well Intermixing (QWI) with passivation of (p-) dopants using hydrogen (or one of its isotypes) , to reduce the absorption of light in a PIC. This is of considerable importance in realising monolithic semiconductor photonic integrated circuits that are both highly manufacturable and can be manufactured at low cost. Furthermore, in comparison to existing PICs fabrication procedures involving highly complex and often repeated processes (photolithography, dry etching followed by epitaxial re-growths) , the present invention considerably lightens the device manufacturing technology by reducing the number of processing steps.
It will also be understood that the invention includes the case where the combination of QWI and hydrogenation is used to form low loss waveguides for use as optical interconnects within a PIC. Finally, it will be further appreciated that the invention includes cases where: the combination of QWI and dopant passivation are used to reduce loss in ' a passive waveguide region in which a cross-section of an optical mode is expanded or compressed in area; light in a passive waveguide is confined in one dimension (slab waveguide) or in two dimensions; a passive waveguide contains a grating- structure, the grating being either a one-dimensional, two- dimensional or three-dimensional structure; the coupling between the grating and the optical field being weak or strong (so-called photonic band-gap structure); the waveguide core, or one or both of the waveguide cladding layers, are composed of multiple Quantum Wells (QWs) or closely multiple Quantum Well (QW) structures known as superlattices ; the multiple Quantum Well (QW) layers optionally being disordered in selected regions to provide band-gap or refractive index changes along or to the sides of the direction of light propagation through the structure; the multiple Quantum Well (QW) layers optionally being doped p-type; active and passive waveguide sections are realized in a single epitaxial growth using patterned dielectric masks (selective-area growth SAG) and subsequently QWI and Hydrogen passivation are selectively applied to the passive section.

Claims

1. A method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure, the method including the steps of :
(a) intermixing at least part of the Quantum Well (QW) structure;
(b) passivating at least some dopants and/or point defects within at least a portion of the device body portion.
2. A method of manufacturing an optical device as claimed in claim 1, wherein the dopants are selected from p-dopants or n-dopants or p- and n-dopants.
3. A method of manufacturing an optical device as claimed in either of claims 1 or 2, wherein step (a) is undertaken before step (b) .
4. A method of manufacturing an optical device as claimed in either of claims 1 or 2 , wherein step (b) is undertaken before step (a) .
5. A method of manufacturing an optical device as claimed in any of claims 1 to 4 , wherein the method of manufacture also includes the preceding steps of: providing a substrate; growing on the substrate : a first optical cladding layer; a core guiding layer including the Quantum Well (QW) structure; and a second optical cladding layer.
6. A method of manufacturing an optical device as claimed in claim 5, wherein the method comprises the step of growing on the second optical cladding layer a contact layer .
7. A method of manufacturing an optical device as claimed in either of claims 5 or 6 , wherein the first optical cladding layer, core guiding layer, and second optical cladding layer and optional top contact layer are grown by Molecular Beam Epitaxy (MBE) or Metal Organic Chemical Vapour Deposition (MOCVD) .
8. A method of manufacturing an optical device as claimed in any of claims 1 to 7, wherein the Quantum Well Intermixing (QWI) step includes the step of: depositing a dielectric layer on at least part of a surface of the device body portion so as to introduce structural defects at least into a portion of the device body portion adjacent the dielectric layer.
9. A method of manufacturing an optical device as claimed in claim 8, wherein the structural defects includes point defects .
10. A method of manuf cturing an optical device- as claimed in either of claims 8 or 9, wherein the dielectric layer is deposited by sputtering.
11. A method of manufacturing an optical device as claimed in claim 10, wherein the dielectric layer is deposited by sputtering using a diode sputterer.
12. A method of manufacturing an optical device as claimed in any of claims 8 to 11, wherein the dielectric layer substantially comprises Silica (Si02) or Aluminium Oxide (Al-03) .
13. A method of manufacturing' an optical device as claimed in claim 11, wherein the sputterer includes a chamber which is substantially filled with an inert gas.
14. A method of manufacturing an optical device as claimed in claim 13, wherein the inert gas is Argon at a pressure of around 2mm of Hg, or a mixture of Argon and Oxygen in the proportion 90%/10%.
15. A method of manufacturing an optical device as claimed in any of claims 1 to 14, wherein the Quantum
Well Intermixing step comprises Impurity-Free Vacancy Disordering (IFVD) .
16. A method of manufacturing an optical device as claimed in any of claims 8 to 14, or claim 15 when dependent upon claims 8 to 14, wherein the Quantum Well Intermixing (QWI) step also includes the subsequent step of annealing the device body portion including the dielectric layer at an elevated temperature.
17. A method of manufacturing an optical device as claimed in either of claims 15 or 16, wherein the method also includes the step of defining a pattern in photoresist on a surface' of the device body portion, depositing the dielectric layer and lifting off the photoresist so as to provide the dielectric layer on the said at least part of the surface of the device body portion .
18. A method of manufacturing an optical device as claimed in claim 17, wherein the method also includes the step of depositing a further dielectric layer on the surface of the device body and on a surface of the dielectric layer prior to annealing.
19. A method of manufacturing an optical device as claimed in claim 18, wherein the further dielectric layer is deposited by a technique other than sputtering.
20. A method of manufacturing an optical device as claimed in claim 19, wherein the other technique is
Plasma Enhanced Chemical Vapour Deposition (PECVD) .
21. A method of manufacturing an optical device as claimed in either of claims 15 or 16, wherein the method includes the steps of depositing a further dielectric layer and then depositing the dielectric layer.
22. A method of manufacturing an optical device as claimed in any of claims 17 to 21, wherein the dielectric layer comprises an intermixing cap and the further dielectric layer comprises an intermixing suppressing cap.
23. A method of manufacturing an optical device as claimed in any of claims 8 to 22, wherein the thickness of the dielectric layer is around lOnm to a few hundred nm.
24. A method of manufacturing an optical device as claimed in claim 16, wherein the annealing step occurs at a temperature of around 700°C to 1000°C for around 0.5 to 5 minutes .
25. A method of manufacturing an optical device as claimed in claim 24, wherein the annealing step occurs at a temperature of substantially 800°C for around 1 minute.
26. A method of manufacturing an optical device as claimed in any of claims 1 to 7 , wherein the Quantum Well Intermixing (QWI) step includes the step of: processing the device body portion so as to create extended defects at least in a portion of the device portion .
27. A method of manufacturing an optical device as claimed in claim 26, wherein said step of processing the device body portion comprises sputtering from the device body portion.
28. A method of manufacturing an optical device as claimed in claim 27, wherein in said step of sputtering from the device body portion a magnetic field is provided around the device body portion.
29. A method of manufacturing an optical device as claimed in either of claims 27 or 28, wherein in said step of sputtering from the device body portion a magnetron sputterer is used.
30. A method of manufacturing an optical device as claimed in any of claims 27 to 29, wherein in said step of sputtering from the device body portion a (reverse) electrical bias is applied across an electrode upon which the device body portion is provided so as to provide a pre-etch and/or cleansing of the device body portion.
31. A method of manufacturing an optical device as claimed in any of claims 26 to 30, wherein the method includes the preceding step of depositing a dielectric layer on at least one other portion of the device body portion .
32. A method of manufacturing an optical device as claimed in claim 31, wherein the method also includes the step of depositing a further dielectric layer on the dielectric layer and/or on the at least one portion of the device body portion.
33. A method of manufacturing an optical device as claimed in claim 32, wherein the dielectric layer and/or the further dielectric layer are deposited by use of a magnetron sputterer.
34. A method of manufacturing an optical device as claimed in claim 32, wherein the dielectric layer and/or the further dielectric layer are deposited by a deposition technique other than by use of a diode sputterer.
35. A method of manufacturing an optical device as claimed in claim 34, wherein the other deposition technique is Plasma Enhanced Chemical Vapour Deposition (PECVD) .
36. A method of manufacturing an optical device as claimed in any of claims 31 to 35, wherein the dielectric layer (s) substantially comprise Silica (Si02) or Aluminium Oxide (A1203) .
37. A method of manufacturing an optical device as claimed in claim 33, wherein the sputterer includes a chamber which is substantially filled with an inert gas .
38. A method of manufacturing an optical device as claimed in claim 37, wherein the inert gas is Argon at a pressure of around 2mm of Hg, or a mixture of Argon and Oxygen in the proportion 90%/l0%.
39. A method of manufacturing an optical device as claimed in any of claims 26 to 38, wherein the Quantum Well Intermixing (QWI) step comprises Impurity-Free Vacancy Disordering (IFVD) .
40. A method of manufacturing an optical device as claimed in any of claims 26 to 39, wherein the Quantum Well Intermixing (QWI) step also includes the subsequent step of annealing the device body portion including the optional dielectric layer at an elevated temperature.
41. A method of manufacturing an optical device as claimed in claim 31 or any of claims 32 to 40 when dependent upon claim 31, wherein the method may comprise the step of : depositing the dielectric layer on a surface of the device body portion; defining a pattern in photoresist on a surface of the dielectric layer and lifting off at least part of the photoresist so as to provide the dielectric layer on said at least one other portion of the device body portion.
42. A method of manufacturing an optical device as claimed in claim 41 when dependent upon claims 32, wherein the method also includes the step of: depositing the further dielectric layer on a portion of the surface of the device body and on a surface of the dielectric layer prior to annealing.
43. A method of manufacturing an optical device as claimed in any of claims 31 to 42, wherein the thickness of the dielectric layer (s) is around lOnm to a few hundred nm .
44. A method of manufacturing an optical device as claimed in any of claims 26 to 43, wherein a subsequent annealing step occurs at a temperature of around 700°C to 1000°C for around 0.5 to 5 minutes.
45. A method of manufacturing an optical device as claimed in any of claim 44, wherein the annealing step occurs at a temperature of substantially 800°C for around 1 minute .
46. A method of manufacturing an optical device as claimed in any of claims 1 to 45, wherein the step of passifying at least some dopants within at least a portion of the device body portion comprises placing the device body portion in a plasma of hydrogen or an isotope of hydrogen or a mixture thereof .
47. A method of manufacturing an optical device as claimed in claim 46, wherein the plasma of hydrogen is a capacitively coupled RF plasma at a pressure of around 0.1 mbar to 100 mbar.
48. A method of manufacturing an optical device as claimed in claim 47, wherein the plasma of hydrogen is at a pressure of around 1 mbar.
49. A method of manufacturing an optical device as claimed in either rof claims 47 or 48, wherein the device body portion is exposed to the plasma of hydrogen for around 10 min to 5 hr .
50. A method of manufacturing an optical device as claimed in claim 49, wherein the device body portion is exposed to the plasma of hydrogen for around 2 hr .
51. A method of manufacturing an optical device as claimed in any of claims 46 to 50, wherein the portion corresponds to a cladding layer of the optical device adjacent to a core layer including the Quantum Well (QW) structure.
52. A method of manufacturing an optical device as claimed in claim 1, wherein a dielectric layer is deposited on at least part of the device body portion prior to step (b) and retained during step (b) .
53. A method of manufacturing an optical device as claimed in claim 1, wherein the intermixing step is carried out by one or more of :
(ii) diffusing a dopant, eg Silicon, Copper, Zinc or Sulphur;
(iii) impurity free vacancy disordering;
(iv) ion implementation, eg of an electrically active dopant or electrically inactive species ; (v) exposure to plasma ,-
(vi) laser melting or laser irradiation intermixing; and (vii) intermixing by diffusion of structure point defects such as from an epitaxial layer.
54. A method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure, the method including the steps of:
(a) intermixing at least part of the Quantum Well (QW) structure;
(b) removing free carriers, eg by passivating dopants and/or point defects, within at least a portion of the device body portion .
55. An optical device fabricated from a method according to any of claims 1 to 54.
56. An optical device as claimed in claim 55, wherein the optical device is an integrated optical device or an optoelectronic device .
57. An optical device as claimed in either of claims 55 or 56, the device body portion is fabricated in a III - V semiconductor materials system.
58. An optical device as claimed in claim 57, wherein the III-V semiconductor materials system is selected from: a Gallium Arsenide (GaAs) based system operating at a wavelength (s) of substantially between 600 and 1300nm; or an Indium Phosphide based system operating at a wavelength (s) of substantially between 1200 and 1700nm.
59. An optical device as claimed in claim 58, wherein the device body portion is made at least partly from Aluminium Gallium Arsenide Arsenide (AlGaAs) , Indium Gallium Arsenide (InGaAs) , Indium Gallium Arsenide Phosphide, (InGaAsP), Indium Gallium Aluminium Arsenide (InGaAlAs) and/or Indium Gallium Aluminium Phosphide
(InGaAlP) .
60. An optical device as claimed in any of claims 55 to
59. wherein the device body portion comprises a substrate upon which are provided a first optical cladding layer, a core guiding layer, and a second optical cladding layer also optionally a low-resistance contact layer.
61. An optical device as claimed in claim 60, wherein the Quantum Well (QW) structure is provided within the core guiding layer.
62. An optical device as claimed in claims 60 or 61, wherein the core guiding layer, as grown, has a smaller band-gap and higher refractive index than the first and second optical cladding layers.
63. An optical device as claimed in claims 60 to 62, wherein the passivated dopants are within the second or the first or the first and second optical cladding layers .
64. An optical device as claimed in claims 55 to 63, wherein the optical device comprises one or more of: a passive waveguide, a slab waveguide or a ridge waveguide, a buried waveguide, a mode expander, mode compressor, or mode converter; a laser diode; an optical modulator; an optical amplifier; an optical switch, or the like, or an Extended Cavity Laser (ECL) , and optionally includes a grating.
65. An optical device providing a device body portion including a Quantum Well (QW) structure as grown, wherein at least part of the Quantum Well (QW) structure is intermixed and at least some dopants within the device body portion are passivated.
66. An optical integrated circuit, optoelectronic integrated circuit (OEIC) , or photonic integrated circuit (PIC) including at least one optical device according to any of claims 55 to 65.
67. A device body portion when used in a method according to any of claims 1 to 54.
68. A wafer of material including at least one device body portion when used in a method according to any of claims 1 to 54.
69. A method of manufacturing an optical device as hereinbefore described with reference to the accompanying drawings .
70. An optical device as hereinbefore described with reference to the accompanying drawings .
71. An optical integrated circuit, optoelectronic integrated circuit (OEIC) or photonic integrated circuit (PIC) as hereinbefore described with reference to the accompanying drawings .
72. A device body portion as hereinbefore described with reference to the accompanying drawings .
73. A wafer of material as hereinbefore described with reference to the accompanying drawings .
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GB2405950A (en) * 2003-09-11 2005-03-16 Agilent Technologies Inc Integrated optical device
GB2405950B (en) * 2003-09-11 2007-05-09 Agilent Technologies Inc Integrated optical device
WO2009045394A1 (en) * 2007-10-01 2009-04-09 Corning Incorporated Quantum well intermixing
US7723139B2 (en) 2007-10-01 2010-05-25 Corning Incorporated Quantum well intermixing
CN101849277B (en) * 2007-10-01 2012-05-09 康宁股份有限公司 Quantum well intermixing
KR101484354B1 (en) 2007-10-01 2015-01-19 코닝 인코포레이티드 A method of quantum well intermixing
CN105390936A (en) * 2015-11-26 2016-03-09 深圳瑞波光电子有限公司 Epitaxial structure and manufacturing method thereof
EP3745471A1 (en) * 2019-05-31 2020-12-02 OSRAM Opto Semiconductors GmbH Method of laser treatment of a semiconductor wafer comprising algainp-leds to increase their light generating efficiency

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WO2003038487A3 (en) 2003-09-04

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