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WO2013055429A2 - Structures de points quantiques pour conversion photovoltaïque efficace et procédés d'utilisation et de réalisation de celles-ci - Google Patents

Structures de points quantiques pour conversion photovoltaïque efficace et procédés d'utilisation et de réalisation de celles-ci Download PDF

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WO2013055429A2
WO2013055429A2 PCT/US2012/048279 US2012048279W WO2013055429A2 WO 2013055429 A2 WO2013055429 A2 WO 2013055429A2 US 2012048279 W US2012048279 W US 2012048279W WO 2013055429 A2 WO2013055429 A2 WO 2013055429A2
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layer
quantum dot
nanomaterial
quantum dots
quantum
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WO2013055429A3 (fr
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Vladimir Mitin
Andrei Sergeyev
Nizami VAGIDOV
Kimberly SABLON
John W. LITTLE
Kitt REINHARDT
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The Research Foundation Of State University Of New York
U.S. Army Research Laboratory
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Publication of WO2013055429A2 publication Critical patent/WO2013055429A2/fr
Publication of WO2013055429A3 publication Critical patent/WO2013055429A3/fr

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/10—Semiconductor bodies
    • H10F77/14—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies
    • H10F77/143—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies comprising quantum structures
    • H10F77/1433—Quantum dots
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
    • H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
    • H10F30/21—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation

Definitions

  • the present invention generally relates to optoelectronic and photovoltaic devices having quantum dots. More particularly, the present invention relates to
  • multi-junction cell which employs multiple junctions where each junction is designed for effective harvesting and conversion of solar energy within a certain window close to its bandgap.
  • a two-junction cell can achieve 42% efficiency and a three -junction cell can convert 49% of solar energy into usable power.
  • an efficiency up to 70% has been predicted.
  • current technology has been limited to triple -junction cells. This is primarily due to technological limitations such as the need for lattice match, thermal expansion match, and current match in cascade of p-n (n-p) junctions as well as high cost of multi-junction devices.
  • the maximum conversion efficiency for unconcentrated radiation realized in multi-junction cells is -32%, which is just slightly above the Shockley-Queisser limit for a single -junction cell.
  • Quantum dots are very promising candidates to create energy level structures for better use of the solar spectrum.
  • the carriers are confined in all three dimensions.
  • the discrete levels may form the bands if dots are close to each other to provide strong interdot coupling.
  • the most popular design of QD solar cells is based on the formation of intermediate bands in the bandgap of the matrix.
  • the band levels of QDs can be tuned by changing QD position in the surrounding matrix.
  • Intermediate band quantum dot solar cells have been intensively investigated during the last decade. In this device the intermediate band is formed from discrete QD levels due to strong tunneling coupling between QDs. Theoretical calculations predict that the intermediate band solar cell can provide an efficiency of -63.2% under full concentration.
  • intensive experimental efforts to improve intermediate band solar cells show that an increase in photovoltaic efficiency has not exceeded 1-2 %.
  • the present technology provides optoelectronic and photovoltaic QD nanomaterials with reduced wetting layer (RWL) and methods that efficiently increase the photoresponse and sensitivity of QD photodetectors as well as improve QD solar cell conversion efficiency.
  • the optoelectronic and photovoltaic nanomaterials exhibit reduced photocarrier capture into QDs and provide improved photoelectron lifetime.
  • This improved photoelectron lifetime increases responsivity and sensitivity of sensors and infrared and terahertz photodetectors.
  • the improved photoelectron lifetime also increases the efficiency of QD solar cells.
  • This approach can be applied to a variety of nanomaterial structures and devices and is scalable because only a part of the material/structure— the wetting layer— is modified. This approach may be combined with other methods to increase the photocarrier lifetime.
  • Figure 1 Capture of photoelectrons from the wetting layer (WL) to quantum dots (QDs) in real space (a) and in band structure presentation (b).
  • FIG. 1 Schematic representation of a nanomaterial with reduced wetting layer (RWL).
  • Figure 3 Schematic representation of a quantum dot IR/THz photodetector with reduced wetting layer.
  • Figure 4 Schematic representation of a quantum dot solar cell with reduced wetting layer.
  • Figure 5 Representative I-V characteristics of quantum dot solar cells and quantum dot solar cells with reduced wetting layer (RWL) under 1 Sun (AM 1.5 G).
  • Figure 6 Representative I-V characteristics of quantum dot solar cells with built-in charge of 2, 3, and 6 electrons per dot under 1 Sun (AM 1.5 G).
  • the present invention provides nanomaterials, methods of making the nanomaterials, and uses of the nanomaterials.
  • the nanomaterials can be used in devices such as optoelectronic and photovoltaic devices. Also provided are methods of making such devices.
  • the present invention is based on the observation that QD materials/structures with a reduced wetting layer exhibit suppression of photocarrier capture.
  • Conventional QD structures have a wetting layer on which QDs are grown.
  • the wetting layer has a large phase volume and consists of a number of electron levels, along which photocarriers may effectively transfer from the interdot space to QDs and then be captured by the QDs due to electron-phonon relaxation ( Figure 1).
  • the devices e.g., optoelectronic and photovoltaic quantum dot devices, have a reduced wetting layer. Without intending to be bound by any particular theory, it is considered these devices exhibit improved performance due to the reduced wetting layer, which is believed to reduce photocarrier capture by QDs and increase the photoelectron lifetime.
  • the present invention provides nanomaterials comprising a plurality of quantum dots and a reduced wetting layer.
  • the nanomaterials can be an optoelectronic nanomaterial or a photovoltaic nanomaterial.
  • reduced wetting layer it is meant the nanomaterials have a wetting layer that is thinner than a nanomaterial having the same structure without a capping material.
  • the wetting layer can be reduced such that it is absent in at least some places.
  • the nanomaterials comprise one or more quantum dot layers, each quantum dot layer comprising: a capping material (a first/bottom layer), a first semiconductor material; a plurality of QDs disposed in the first semiconductor material; a capping material (a second/top layer); and a spacer layer of second semiconductor material that is doped such that the quantum dots have built-in charge and is disposed between adjacent quantum dot layers.
  • the nanomaterial is disposed on a semiconductor substrate.
  • the substrate can comprise one or more layers of semiconductor material.
  • the substrate can have a broad range of thicknesses.
  • the layers can, each independently, be from 0.2 micrometers to 10 micrometers, including all values to the 0.1 micrometer and ranges therebetween.
  • the individual layers can be n-doped or p-doped as desired. The doping level is within the purview of one having skill in the art.
  • the semiconductor substrate can be any semiconductor material on which the QD layers can be formed.
  • the substrate can have a range of sizes and shapes. Examples of suitable materials include, but are not limited to, GaAs, InP, Si, BaF 2 , CaF 2 , or SiC.
  • An example of a substrate is a Si or GaAs wafer suitable for use in semiconductor fabrication processes known in the art.
  • the QDs are present individually or as clusters of QDs.
  • the QDs are present as individual quantum dots, quantum dot clusters, or a combination of quantum dots and quantum dot clusters.
  • the QD clusters are groups of QDs and each cluster is separated by a distance which exceeds the interdot space in an individual cluster. If the QDs are present as clusters of QDs, each QD layer has at least one cluster of QDs.
  • the nanomaterial can have a range of QDs per cluster and QD clusters per layer.
  • the number of QDs per cluster and number of QD clusters per layer can vary depending on the QD materials and doped semiconductor material.
  • the QDs per cluster can be from 2 to 15, including all integer numbers of QDs therebetween.
  • the number of clusters per layer can be from 10 8 to 10 12 , including all values to the 100 clusters per layer and ranges therebetween.
  • the distance between nearest QDs in a cluster can vary.
  • the distance between nearest dots in a cluster is the shortest distance from the nearest boundaries of nearest QDs in a cluster.
  • the distance can be from 1 to 5 nm.
  • the distance between nearest QD clusters can also vary.
  • the distance between nearest QD clusters is the shortest distance from the boundaries of nearest QD clusters.
  • the distance between nearest QD clusters can be from 3 to 5 times the distance between nearest QDs in the clusters.
  • the QDs are vertically correlated.
  • vertical correlation or “vertically correlated” it is meant that, with respect to QD clusters, the centers of QD clusters in a QD layer are correlated to corresponding centers of QD clusters in an adjacent layer, and with respect to individual QDs, that individual QDs are correlated with
  • adjacent layers it is meant a first QD layer and a second QD layer directly above or below the first QD layer. Adjacent layers are not in physical contact with each other (e.g., the adjacent layers are separated by a layer or layers that are not QD layers such as a spacer layer). In various embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% of the QDs are vertically correlated with corresponding QDs.
  • At least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% of the centers of QD clusters are vertically correlated with corresponding QD clusters. In other various embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% of the QDs are vertically correlated with corresponding QDs, and centers of QD clusters are vertically correlated with corresponding centers of QD clusters. In another embodiment, all of the QDs are vertically correlated. In yet another embodiment, all of the QD clusters are vertically correlated. In another embodiment, all of the QDs are vertically correlated and all of the QD clusters are vertically correlated.
  • the average distance between centers of the nearest (i.e., shortest distance between two dot clusters) QD clusters in adjacent layers is 70% or less than that in the case of random distribution of cluster centers. In other words, less than
  • N c i is the concentration of QD clusters in a QD layer and b is the distance between layers.
  • the average distance between centers of the nearest QD clusters in adjacent layers is 50% or less, 40% or less, 30% or less, 20 % or less, 10% or less, 5% or less, or 1% or less than in the case of random distribution of cluster centers.
  • the average distance between the QDs in adjacent layers is 70% or less than that in the case of random distribution of QDs in the
  • n is the QD concentration in a QD layer and b is the distance between layers.
  • the average distance between the positions of the nearest individual QDs in adjacent layers is 50% or less, 40% or less, 30% or less, 20 % or less, 10% or less, 5% or less, or 1% or less than in the case of random distribution of individual QD positions.
  • the nanomaterial has one or more QD layers. Each QD layer has individual
  • the QD layer can have QDs and semiconductor material filling the interstitial space around the QDs.
  • the quantum dots disposed in the semiconductor material is a planar layer of quantum dots disposed in a layer of semiconductor material.
  • the quantum dots disposed in the quantum dot medium can be a planar layer of quantum dots in a layer of n- doped semiconductor material.
  • the quantum dots can be randomly placed in the QD layer.
  • the positions of the quantum dots in the QD layer are not regular.
  • the nanomaterial can have from 1 to 100 such layers, including all integer numbers of layers and ranges therebetween.
  • the QD layer has a layer of the QD material (e.g., a monolayer of the QD material) and the QDs are in contact with the layer of QD material.
  • the quantum dots can be formed from various materials and have a wide range of dimensions provided the QDs have energy levels to absorb IR energy in the solar spectrum.
  • the QDs absorb at least a portion of energy having a wavelength of 700 nm to 1 mm, including all values to the nm and ranges therebetween.
  • suitable materials include, but are not limited to, InAs, GaAs, Ge, SiGe, CdS, InP, PbSe, GaN, or a combination thereof.
  • the height, width, and areal density of the quantum dots depends on the materials and growth conditions used to form the quantum dots and are not limited to any specific range.
  • quantum dots have a height (measured normal to the surface on which the quantum dots are disposed) of from 2 nm to 10 nm, including all values to the nm and ranges therebetween. For example, a height of from 3 nm to 5 nm is desirable for InAs quantum dots.
  • the length and width of the quantum dots can be from 10 nm to 40 nm, including all values to the nm and ranges therebetween.
  • a broad range of quantum dot densities can be used.
  • the density of quantum dots can be from
  • the quantum dots can be formed by methods known in the art.
  • the quantum dots can be formed by self-assembly methods.
  • self-assembly methods include the Stranski-Krastanow and Volmer- Weber methods, in which self-assembled quantum dots are formed during crystal growth with metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).
  • MOCVD metalorganic chemical vapor deposition
  • MBE molecular beam epitaxy
  • a wide range of quantum dot size (e.g., length, width, and height) distribution can be used.
  • the relative full- width at half maximum (FWHM) of the quantum dot size (e.g., length, width, or height) distribution can be from 10% to 70%, including all integer % values and ranges therebetween.
  • QDs with built-in charge QDs disposed in a layer of semiconductor material that is n-doped.
  • the amount of dopant is such that the QDs are at least partially filled by electrons for n-doped semiconductor materials, thus providing QDs with built-in charge.
  • the charge in the QDs creates potential barriers which prevent photoelectron capture by the QDs and/or the electrons in the charged dots provide electron coupling to infrared radiation.
  • Optoelectronic devices based on the nanomaterials can have increased photoelectron lifetime and improved coupling to IR radiation due to the QDs with built-in charge.
  • the thickness of an individual QD layer can vary.
  • the thickness of an individual QD layer can be from 2 nm to 10 nm, including all values to the nm therebetween.
  • the thickness of the QD layer is equal to the height of the largest QD in the layer.
  • the capping material is disposed on the layer of quantum dots (e.g., a second layer of capping material).
  • the QDs are disposed on a layer of capping material (e.g., a first layer of capping material).
  • the capping material can be present as a continuous layer of material or a discontinuous layer of material.
  • the first and second layers of capping material can be the same or different materials.
  • the capping material can be a semiconductor material. The material has a wider band gap than of the quantum dot material and of the semiconductor material which separate quantum dot layers.
  • the capping material is AlGaAs
  • the quantum dot material is InGaAs
  • the capping material is AlGaAs
  • the quantum dot material is InGaP
  • the capping material is AlGaP.
  • the material covers at least a portion of a surface of the quantum dots. In various embodiments, the material covers at least a portion of a surface of 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the quantum dots. In an embodiment, the material covers at least a portion of a surface of all of the quantum dots.
  • the thickness of the capping material is from 1 to 4 nm, including all values to the 0.1 nm and ranges therebetween.
  • the thickness refers to an average thickness over the entire layer or a thickness of a region of the layer (an area less than the area of the entire layer).
  • This thickness of the capping material can alternatively be expressed in terms of atomic monolayers.
  • the thickness of the capping material can be from 3 to 14 atomic monolayers. Examples of suitable capping materials include AlGaAs, AlGaP, AlAs, and A1P.
  • the wetting layer is a quantum dot material in the inter quantum dot space.
  • the wetting layer is the residual material remaining after self-assembly formation of quantum dots from a layer of quantum dot material. Without intending to be bound by any particular theory, it is considered the presence of the capping material results in a reduction of the wetting layer.
  • different surface diffusion parameters of In and Al atoms result in different growth pattern of InAs and AlGaAs on pyramidal QD coverage. While less mobile Al atoms result in formation of conformal AlGaAs layers, In atoms are driven to lower-stress regions.
  • the wetting layer is reduced (e.g., the layer has fewer atomic monolayers of material) relative to the wetting layer of nanomaterial that does not have capping material.
  • the wetting layer is typically from 1, 2, or 3 atomic monolayers. Accordingly, in various embodiments, the wetting layer is reduced by 1, 2, or 3 atomic monolayers. In an embodiment, the wetting layer is completely removed. When the wetting layer is completely removed the quantum dots in the area where the wetting layer is reduced the quantum dots have no continuous quantum dot material between adjacent quantum dots. The wetting layer can be reduced over a portion of the wetting layer area or over the entire layer area. In various embodiments, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the area of the wetting layer is reduced. In an embodiment, at least 30% of the quantum dots have no continuous quantum dot material between adjacent quantum dots.
  • the wetting layer may not be uniform across a quantum dot layer.
  • the reduction in thickness of the wetting layer can be considered as a reduction in the average wetting layer across a QD layer or as a reduction in a discrete area of the QD layer (less than the entire QD layer).
  • the presence or absence of a wetting layer can be determined by, for example, photoelectron spectroscopy.
  • intermediate bands there is no requirement that intermediate bands be formed. It is considered that having multiple QD layers where the distance between the QD layers is greater than 30 nm will not result in intermediate band formation.
  • the nanomaterial and/or device comprising the nanomaterial does not have intermediate bands.
  • the thickness of the layers is such that intermediate bands are not formed.
  • the thickness of the spacer layers is large enough (e.g., 20 nm or greater in InAs QD/GaAs structures) to minimize stress and formation of defects, which increases recombination losses.
  • the spacer layers between adjacent QD layers are doped semiconductor materials.
  • the spacer layers do not contain QDs.
  • the semiconductor material can be n-doped.
  • the thickness of individual spacer layers can be from 15 nm to 50 nm, including all values to the nm and ranges therebetween.
  • the spacer layer can be formed by methods known in the art.
  • the n-doped layer of semiconductor material can be produced during the formation of the semiconductor material layer using MBE or MOCVD methods.
  • the doping level can correspond to two electrons per dot to thirty electrons per dot, including all integer electrons per dot values and ranges therebetween.
  • the spacer layer is doped such that the dopant concentration in the layer is equivalent to at least two electrons per dot, at least three electrons per dot, at least four electrons per dot, at least five electrons per dot, or at least six electrons per dot. Without intending to be bound by any particular theory, it is considered that conversion efficiency improves if the doping level corresponds to two or more electrons per dot.
  • the device has a doping level corresponding to six electrons per dot and exhibits a 50% increase in efficiency compared to devices that have layers which are not n-doped.
  • the n-dopant in the spacer layer is substantially localized in a discrete region of the semiconductor material.
  • This discrete region can have a thickness of from 1 nm to 100 nm, including all values to the nm and ranges therebetween.
  • this discrete region can be a selectively-doped layer or a ⁇ -doped layer (dopant atoms confined to a discrete region) within the QD layer.
  • devices with such regions or layers have increased potential barriers around the dots. Such devices have increased conversion efficiency as compared to the same device without such n-doping.
  • substantially localized it is meant at least 90% of the n-dopant in the QD medium layer is in a discrete region or a discrete sub-layer of the semiconductor material. In various embodiments at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% of the n-dopant is in the region or layer of the semiconductor material.
  • the spacer layer comprises a discrete sub-layer (e.g., a selectively-doped layer or a ⁇ -doped layer) of n-doped semiconductor material in a layer of semiconductor material.
  • the n-dopant in the spacer layer is only in a discrete region or discrete sub-layer (e.g., a selectively-doped layer or a ⁇ -doped layer) of the semiconductor material.
  • the ⁇ -doped layer can have a thickness of from 1 nm to 10 nm, including all values to the nm and ranges therebetween.
  • the ⁇ -doped layer boundary can be a distance of from greater than or equal to 5% of the total thickness of the layer of
  • the ⁇ -doped layer boundary can be from 5 nm or greater from either boundary of the spacer layer.
  • the center of the ⁇ -doped layer is substantially equidistant from either boundary of the spacer layer.
  • substantially equidistant it is meant that the center of the ⁇ -doped layer is at a distance of 10% or less of the total thickness of the QD medium layer from the center of the QD medium layer.
  • the center of the region is at a distance of 5% or less to 1% or less from the center of the layer.
  • the nanomaterials exhibit desirable properties.
  • the nanomaterials exhibit a photoelectron lifetime that is at least 10 times, 20 times, 25 times, or 30 times greater than that exhibited by a comparable nanomaterial without a reduced wetting layer.
  • the nanomaterials can have improved properties relative to bulk semiconductors, low-dimensional semiconductors, and quantum well structures.
  • the nanomaterials exhibit a photoelectron lifetime and/or photoconductive gain and/or responsivity that is at least 10 times, 25 times, 50 times, 100 times, 500 times, or 1000 times greater than that exhibited by comparable bulk semiconductors, low-dimensional semiconductors, and quantum well structures, if such properties are exhibited by the particular nanomaterial.
  • the nanomaterials exhibit a sensitivity (which can be measured as noise equivalent power or detectivity) that is at least 10 or at least 100 times greater than that exhibited by comparable bulk semiconductors, low-dimensional semiconductors, and quantum well structures, if such a property is exhibited by the particular nanomaterial.
  • the present invention provides methods of making the nanomaterials described herein.
  • the methods comprise a step of depositing a layer of capping material on a quantum dot layer.
  • the methods comprise a step of depositing a layer of capping material and depositing a layer of QD material thereon. This step provides a nanomaterial having a reduced wetting layer.
  • the method comprises the steps of: a) depositing a layer of a first semiconductor material (spacer layer); b) depositing a (first, e.g., bottom) layer of a capping material having a wider band gap than the band gap of the quantum dot material and of the semiconductor material; c) depositing a layer of quantum dot material such that a plurality of quantum dots and a wetting layer are formed; d) depositing a (second, e.g., top) layer of capping material having a wider bandgap than the band gap of the quantum dot material and of the semiconductor material such that at least a portion of a surface of 30% of the quantum dots is covered by the (first/bottom) layer of capping material and the thickness of the wetting layer is reduced; e) depositing a layer of a second semiconductor material (e.g., the spacer layer); f) n-doping the layer of second semiconductor material such that the layer has built-in charge; and optionally, repeat
  • the semiconductor materials can be deposited by methods known in the art.
  • the layers of semiconductor material can be deposited by MBE or MOCVD methods.
  • the layers can be doped if desired.
  • the layers can be doped (e.g., n-doped or p- doped) by methods known in the art.
  • the layers can be doped during deposition or after deposition.
  • the spacer layer of semiconductor material is deposited such that the n-dopants are in a discrete region of the layer of semiconductor material as described herein.
  • the quantum dot material is the material from which the quantum dots are formed. For example, a layer of InAs is deposited to form InAs quantum dots.
  • the quantum dot material can be deposited by methods known in the art.
  • the layer of second semiconductor material is selectively doped.
  • an n-doped layer of second semiconductor material can be formed by depositing a discrete region (e.g., a selectively-doped layer or a ⁇ -doped layer) of n-doped second semiconductor material as part of the deposition of the layer of second semiconductor material.
  • the nanomaterial with reduced wetting layer is fabricated by: a. depositing a first layer of second semiconductor material; b. depositing a capping layer (first/bottom layer); c. depositing a layer of quantum dot material such that a plurality of quantum dots is formed; d. depositing a capping layer (second/top layer); e.
  • steps a., b., c, d., e., f., and g. are repeated.
  • the steps of the method can be repeated to form structures (or devices) having multiple layers of nanomaterials (or quantum dot layers). For example, the steps of the method can be repeated from 1 to 100 times, including all integers and ranges therebetween.
  • the quantum dots can be formed by a variety of methods known in the art.
  • the quantum dots can be formed using methods based on self-assembly, such as, for example, the Stranski-Krastanow or Volmer- Weber methods.
  • the Stranski-Krastanow method is an epitaxial method that efficiently creates a lattice-mismatch strain between the dots and the bulk matrix while minimizing lattice damage and defects.
  • the self-assembled quantum dots appear spontaneously, substantially without defects, during crystal growth with MOCVD or MBE.
  • MOCVD Metal Organic Chemical Vapor
  • MBE Metal-vapor deposition
  • the quantum dots are deposited by a self-assembly method.
  • 1.7 to 3.5 monolayers of a material such as InAs is deposited on a layer of semiconductor material such that quantum dots grow spontaneously.
  • the InAs two- dimensional material left after quantum dot growth is referred to as a wetting layer.
  • the wetting layer has width of 1, 2, or 3 atomic monolayers. Because of the thickness of the wetting layer, quantization of the transverse motion leads to a single energy level. Photocarriers on this level may transfer quasi-classically along the wetting layer.
  • the capping material can be deposited by methods known in the art.
  • the capping material is deposited to form a layer on the formed quantum dots and wetting layer.
  • the capping material is also deposited to form a layer of capping material on which the layer of quantum dot material is deposited (and the quantum dots formed).
  • the capping material can be deposited by MBE or MOCVD deposition methods.
  • the capping material is deposited such that each quantum dot is discrete having no continuous quantum dot material between adjacent quantum dots.
  • QD structures with RWL can be fabricated by growing InAs
  • the thin AlGaAs layers which are used to initiate InAs QD formation, radically reduce the InAs wetting layer, almost eliminating it.
  • measurements show detectable decrease of photoluminescence intensity related to transitions from the wetting layer to quantum dots. It means that wetting layer is detectably reduced in these structures.
  • the method can comprise additional steps.
  • the method can comprise deposition of layers such as electrodes, anti-reflecting coatings, and back-surface field barriers.
  • An example of a method to provide a reduced wetting layer is to grow InAs quantum dots on a narrow (1-2 nm) capping layer (bottom layer) of AlGaAs which has a wider band gap than the InAs and GaAs that separates adjacent quantum dot layers. After the formation of InAs quantum dots, they are covered by a narrow (1-2 nm) capping layer (top layer) of AlGaAs as shown in Figure 2.
  • the composite second layer may be repeated N-times (see Figure 2). N can be 1 to 100, including all integer values and ranges therebetween.
  • the present invention provides optoelectronic devices (e.g. sensors, THz and IR photodetectors) that have desirable photoelectron lifetime.
  • the IR/THz photodetector comprises a substrate on which a stack of layers is disposed (see Figure 3).
  • the first layer is n-doped semiconductor material.
  • the next is the nanomaterial with reduced wetting layer.
  • the significant charging of QDs in this nanomaterial is realized by n-doping of the semiconductor layer (n-doped layer in Figure 3).
  • the third layer is an n-doped semiconductor material.
  • the spectral characteristics of the photodetector are determined by the selection of QD materials, capping and spacer layers, the size of QDs, and thicknesses of other layers. Reduced wetting layer provides longer photocarrier lifetime, which in turn enhances the photoresponse and decreases the generation-recombination noise, and in this way increases the sensitivity of the detector.
  • the present invention provides photovoltaic devices (e.g. solar cells and thermophotovoltaic devices) that have desirable photoelectron lifetime.
  • the photovoltaic device comprises a substrate on which a stack of layers is disposed (see Figure 4).
  • the first layer is n-doped semiconductor material.
  • the next is the nanomaterial with reduced wetting layer.
  • the significant charging of QDs in this nanomaterial is realized by n- doping of the semiconductor layer (n-doped layer in Figure 4).
  • the third layer is p-doped semiconductor material.
  • the present invention provides uses of the nanomaterials described herein.
  • the nanomaterials can be used in devices such as optoelectronic and photovoltaic devices.
  • the devices can be made using techniques known in the art.
  • the device is an optoelectronic device.
  • the devices are optoelectronic devices such as semiconductor detectors (e.g., IR and THz detectors).
  • the devices may also have a substrate and a layer or layers of semiconductor material (e.g., spacer layers between the QD layers and the contacts).
  • the individual layers can, individually, each be n-doped semiconductor material or an undoped semiconductor material.
  • the layers (e.g., a stack of layers) of the nanomaterial can be disposed on a substrate.
  • the device comprises the nanomaterial.
  • the substrate can be any semiconductor material on which the stack of layers can be formed.
  • the substrate can have a range of sizes and shapes. Examples of suitable materials include, but are not limited to, GaAs, InP, Si, BaF 2 , CaF 2 , or SiC.
  • An example of a substrate is a Si or GaAs wafer suitable for use in semiconductor fabrication processes known in the art.
  • the layers of semiconductor materials, which are not spacer layers, in the devices can be formed from a variety of semiconductor materials.
  • suitable semiconductor materials include, but are not limited to, GaAs, InP, Si, BaF 2 , CaF 2 , and SiC.
  • the semiconductor layers can have a broad range of thicknesses.
  • the layers can, each independently, be from 0.2 micrometers to 10 micrometers, including all values to the 0.1 micrometer and ranges therebetween.
  • the optoelectronic device can comprise other layers.
  • the device can comprise layers such as electrodes and anti -reflecting coating layer.
  • the photovoltaic device can comprise other layers.
  • the device can comprise layers such as electrodes, anti-reflecting coating layer, and back- surface field barriers.
  • the device can be used in combination with solar energy concentrators.
  • the device is a semiconductor detector (e.g., a photodetemiconductor detector (PDI), a photodetemiconductor detector (PDI), or a photodetemiconductor detector (PDI), or a photodetemiconductor detector (PDI), or a photodetemiconductor detector (PDI).
  • a semiconductor detector e.g., a photodetemiconductor detecting a semiconductor detector.
  • the device comprises metallic contacts and, optionally, spacer layers between which the nanomaterial and contacts are disposed.
  • An example of a method for making an optoelectronic device comprises the steps of: a) providing a semiconductor substrate; b) depositing a layer of n-doped first semiconductor material; c) depositing the nanomaterial (of claim 1) having a reduced wetting layer; and d) depositing a layer of n-doped second semiconductor material.
  • An example of a method for making a photovoltaic device comprises the steps of: a) providing a semiconductor substrate; b) depositing a layer of n-doped first
  • nanomaterial can be deposited by one of the methods disclosed herein. In these examples, the semiconductor materials and quantum dot materials are described herein.
  • the devices exhibit desirable characteristics.
  • the optoelectronic devices exhibit longer photocarrier lifetime and higher photoresponse.
  • the photovoltaic device exhibits a short circuit current of at least 30 mA/cm 2 .
  • the methods of making the devices can comprise additional steps.
  • the method can comprise deposition of layers such as electrodes, anti-reflecting coatings, and back-surface field barriers.
  • the devices can demonstrate improved harvesting of IR energy.
  • devices of the instant invention show an improvement of 50% of efficiency due to conversion of IR energy.
  • the device is a photovoltaic device exhibiting an improved conversion efficiency of at least 5%, 10%, 20%, 30%, 40% or 50%, as compared to a photovoltaic device that does not have quantum dots with built-in charge.
  • the devices can also demonstrate improved short circuit, Jsc, values.
  • the short circuit current density of the device increases to 24.3 mA/cm 2 without deterioration of the open circuit voltage, compared to 15.1 mA/cm 2 in an undoped solar cell.
  • the short circuit, Jsc, values for quantum dot GaAs devices are from 15 mA/cm 2 to 35 mA/cm 2 , including all values to the mA/cm 2 and ranges therebetween.
  • This example provides an example of a photovoltaic device with a reduced wetting layer.
  • quantum dot structures with RWL were fabricated.
  • the built-in charge was realized by S- doping in the middle of each GaAs layer that separates the dot layers.
  • the structures contain 20 stacks of InAs QD layers grown on thin AlGaAs capping layers.
  • the QD layers are capped by AlGaAs layers and separated by GaAs with various dopant sheet densities providing zero, two, three, four, and six electrons per QD, respectively (based on average dot densities measured with transmission electron microscopy).
  • the thickness of the GaAs spacer layer was 50 nm for all samples.
  • the spacer thickness was chosen in an effort to dissipate strain fields in subsequent layers and, hence, reduce the strain accumulation and dislocations in the multi-stack samples.
  • the ⁇ + - ⁇ - ⁇ + structure (where ⁇ refers to the ⁇ -doped QD
  • p-Alo.45Gao.55As with a doping density of 5x10 cm "
  • a 50 nm p-GaAs contact layer with a doping density of 5xl0 18 cm “3 .
  • 250 ⁇ circular solar cells were fabricated using photolithography and mesa etching.
  • the structure used bottom n-type blanket metallization of Au/Sn/Au and Cr/Au top p-type ring contact.
  • the contact ring diameter was 200 ⁇ with a 100 ⁇ opening in the center to allow for top-side illumination.
  • I-V characteristics of QD solar cells were measured using calibrated solar simulator (Model 16S-300-002 Air Mass Solar Simulator).
  • a set of I-V curves for quantum dot solar cells and quantum dot solar cells with reduced wetting layer are shown in Figure 5.
  • the implementation of structures with reduced wetting layer increases the short circuit current from 18 mA/cm 2 to 36 mA/cm 2 .
  • These data are for quantum dot structures with built-in charge of approximately three electrons per dot.
  • quantum dot technology provides increase of the short circuit current from 15 mA/cm 2 to 24 mA/cm 2 ( Figure 6) and quantum dot RWL provides additional increase up to 36 mA/cm 2 ( Figure 5).
  • the effect provided by the reduced wetting layer is complementary to quantum dot technology and (ii) it provides an additional increase of the conversion efficiency.

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  • Photovoltaic Devices (AREA)

Abstract

La présente invention porte sur des nanomatières ayant une couche de mouillage réduit, des procédés de réalisation des nanomatières et des utilisations des nanomatières. Les nanomatières ayant une couche de mouillage réduit peuvent être utilisées dans des dispositifs optoélectroniques et des dispositifs photovoltaïques. Les nanomatières comprennent une couche de couverture qui conduit à en une couche de mouillage réduit. Les dispositifs ayant une couche de mouillage réduit présentent une durée de vie du photoélectron plus longue qui augmente la réactivité et la sensibilité de détecteurs et le rendement de conversion de dispositifs photovoltaïques.
PCT/US2012/048279 2011-07-28 2012-07-26 Structures de points quantiques pour conversion photovoltaïque efficace et procédés d'utilisation et de réalisation de celles-ci WO2013055429A2 (fr)

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JP2017126622A (ja) * 2016-01-12 2017-07-20 シャープ株式会社 間接遷移半導体材料を用いた量子構造を有する光電変換素子

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WO2008030183A1 (fr) * 2006-09-08 2008-03-13 Agency For Science, Technology And Research Diode électroluminescente à longueur d'onde accordable
US20090255580A1 (en) * 2008-03-24 2009-10-15 Neil Dasgupta Quantum dot solar cell with quantum dot bandgap gradients
US20100243053A1 (en) * 2007-06-26 2010-09-30 Seth Coe-Sullivan Photovoltaic devices including quantum dot down-conversion materials useful for solar cells and materials including quantum dots
US20110143475A1 (en) * 2008-06-06 2011-06-16 Universidad Politécnica de Madrid Method for manufacturing of optoelectronic devices based on thin-film, intermediate-band materials description

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WO2008030183A1 (fr) * 2006-09-08 2008-03-13 Agency For Science, Technology And Research Diode électroluminescente à longueur d'onde accordable
US20100243053A1 (en) * 2007-06-26 2010-09-30 Seth Coe-Sullivan Photovoltaic devices including quantum dot down-conversion materials useful for solar cells and materials including quantum dots
US20090255580A1 (en) * 2008-03-24 2009-10-15 Neil Dasgupta Quantum dot solar cell with quantum dot bandgap gradients
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017126622A (ja) * 2016-01-12 2017-07-20 シャープ株式会社 間接遷移半導体材料を用いた量子構造を有する光電変換素子

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