WO2004022820A1 - Method for achieving device-quality, lattice- mismatched, heteroepitaxial active layers - Google Patents
Method for achieving device-quality, lattice- mismatched, heteroepitaxial active layers Download PDFInfo
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- WO2004022820A1 WO2004022820A1 PCT/US2002/028314 US0228314W WO2004022820A1 WO 2004022820 A1 WO2004022820 A1 WO 2004022820A1 US 0228314 W US0228314 W US 0228314W WO 2004022820 A1 WO2004022820 A1 WO 2004022820A1
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- layer
- active layer
- heterostructure
- buffer
- inasypi
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
Definitions
- This invention relates generally to heteroepitaxial lattice-mismatched systems and, more particularly, it relates to optimizing the material quality of an active region that is lattice-mismatched to a particular substrate.
- the invention uses a compositional step-grade that is terminated with a strained buffer layer correctly lattice-matched to the active layer of interest.
- An intermediate region serves to isolate the active layer from the underlying misfit-dislocation networks, and to prevent threading dislocations from reaching the active region.
- Lattice-mismatched heteroepitaxy offers numerous film/substrate combinations for semiconductor device design. Many applications require optically thick, mismatched films with device-quality electronic properties, such as adequate minority-carrier lifetime.
- strain relaxation generates dislocations that limit carrier-transport behavior via Shockley-Read-Hall recombination. Residual strain can also deteriorate surface planarity and cause wafer bowing, hindering processing control.
- Fundamental studies have identified the benefits of multilayers and lattice-mismatched heterointerfaces to filter threading dislocations and control the formation of misfit-dislocation networks that promote relaxation.
- the alloy composition of the buffer layer material such that the lattice constant of the buffer layer when fully relaxed of strain is matched to that of the active layer material when fully relaxed of strain.
- the buffer layer displaces the active layer from the underlying misfit dislocation networks, which generate inhomogenous strain fields, and also limits the propagation of threading dislocations, which typically decrease in density as the layer thickness is increased.
- Lattice mismatch among electronic materials remains a primary limitation in the design of high-performance, thin-film devices. Many applications require deposition of a material with a particular physical property, such as the optical bandgap for light absorption or emission. Heteroepitaxy uses the structure of the substrate surface as a crystallographic template for nucleation and growth of thin films with high material quality. Although the constituent materials may have similar crystal structures parallel to the growth plane, slight differences in their bulk lattice parameters introduces lattice mismatch that is accommodated by a combination of strain and dislocations.
- the equilibrium structures of most tetrahedral semiconductor materials can be described in terms of a single, cubic lattice parameter.
- the cubic lattice parameters of the pseudobinary semiconductor alloys vary with composition.
- the bulk misfit / of an epitaxial film is defined in terms of the equilibrium film and substrate lattice constants, a and as , respectively, as: f ⁇ ala s -l (1).
- a compositionally graded region and/or buffer layer can be used to provide a "virtual" substrate with the desired lattice constant for subsequent deposition of an active layer. Relaxation occurs within the graded region, with both a corresponding diminution of structural coherence in electronically inactive depths of the film, and the generation of undesirable topography and threading dislocations. The extent and mechanisms of layer relaxation are sensitive to the particular mechanical properties and growth conditions of the constituent materials.
- Biaxial strain arises in lattice-mismatched thin films of semiconductor alloys.
- the in-plane component of the strain field (parallel to the growth plane) is given by where ⁇ is the in-plane lattice parameter for the strained layer.
- the in-plane misfit which is an indication of the coherence between the film and substrate, is defined as:
- f differs from the bulk misfit in the presence of strain, and is proportional to the misfit dislocation density at the film/substrate interface.
- the bulk lattice constant of the buffer layer is lattice-matched to that of the active layer.
- coherence is maintained between the active layer and the buffer layer in the prior art, residual strain adversely affects the planarity of the epitaxial growth surface, limiting the maximum allowable film thickness.
- the active layer should be structurally isolated from the graded region to reduce the influence of misfit dislocations on the active layer, and to reduce the density of threading dislocations that penetrate the active layer.
- the optimal alloy composition of the buffer layer is that which, when in a state of strain induced by epitaxial growth, has a lattice constant parallel to the substrate that is equal to that of the unstrained active layer. Furthermore, an intermediate region between the buffer layer and the active layer is included, which serves to displace the active layer from the graded region, thereby reducing the influence of underlying dislocations on the active layer. is used for a number of low-bandgap device applications, including thermophotovoltaic power generation.
- Lattice-matched 0 ⁇ 7) double heterostructures (DHs) on InP show minority-carrier lifetimes typically in the range of -10-20 ⁇ s.
- InAsyPi y is an ideal candidate for compositional grading from P substrates, and provides carrier confinement and surface passivation to Ga ⁇ In ⁇ - ⁇ : As , with optical transparency for infrared applications.
- This invention provides specific criteria for the structural optimization of Ga x In 1-x As/InAsyPi-y DHs grown on h P substrates using a compositional grade with a strained buffer layer.
- the present invention discloses a heterostructure and a method for minimizing dislocations and residual strain resulting from lattice mismatch of a heteroepitaxial layer.
- the method comprises providing a substrate, depositing a compositionally step-graded region on the substrate, terminating the step-grade with a a buffer layer of extended thickness, depositing an intermediate region on the buffer layer, depositing an active layer on the intermediate region, and depositing a capping layer on the active layer.
- the method uses a buffer layer of selected alloy composition.
- the buffer layer is in a state of biaxial strain that causes the in-plane lattice constant of the buffer layer to match precisely the unstrained lattice constant of the active layer.
- An intermediate region containing a displacement layer is inserted between the buffer and active layers to spatially separate the active layer from the misfit dislocation networks that reside in the graded region, and to limit the propagation of threading dislocations into the active region.
- the elimination of residual strain within the active layer is desirable for developing complex multilayer heterostructures, such as tandem thermophotovoltaic devices.
- FIG. 1 is a sectional view illustrating a semiconductor consisting of a semi-insulating substrate, a compositionally step-graded region containing a buffer layer, an intermediate region, an active layer, and a thin capping layer, constructed in accordance with the present invention
- FIG. 2 is a composite depicting the results of X-ray diffraction measurements of the lattice constant a( ⁇ ) vs.
- ⁇ is the tilt from the substrate normal, for five different Ga ⁇ In ⁇ - ⁇ :As (GafriAs) active layers and the underlying InAsyPi-y (InAsP) buffer layers, and the transmission electron micrographs showing the dislocation morphology in the vicinity of the interface between the GalnAs active layer and the buffer layer.
- FIG.3 is a graph illustrating minority-carrier lifetime ⁇ measured by photoconductive decay vs. ⁇ f' measured by X-ray diffraction
- FIG.4 is a plot of the experimental strain in the Ga ⁇ In 1- ⁇ : As active layer vs. ⁇ .
- the solid line through the data is a least-squares fit.
- the small open circle indicates the optimized structure; the small open square indicates the prior art.
- FIG. 5 is a graph of idealized misfit profiles for an optimized DH showing the bulk, unstrained misfit / for the fully relaxed layers, and the strained, in-plane misfit / as functions of position with respect to the substrate surface using the optimized heterostructure design;
- FIG. 6 is a schematic diagram illustrating the invention concept:
- a strained buffer layer provides a lattice-matched template for the coherent growth of an unstrained active layer.
- An intermediate region is inserted between the step-graded and active regions for structural isolation.
- the thin, cross-hatched lines represent crystallographic planes.
- the partially coherent interface structure below the buffer layer has been simplified for clarity. Relevant parameteric relationships corresponding to various layers and interfaces are listed to the right of the diagram.
- DHs containing the semiconductor alloys Ga ⁇ In 1- ⁇ As and InAsyPi-y on hiP substrates, indicated generally at 10, are prepared by metalorganic vapor-phase epitaxy (MOVPE).
- MOVPE metalorganic vapor-phase epitaxy
- the structures are designed with the following components: (a) a semi-insulating h P substrate 12, (b) a compositionally step-graded layer of InAsyPi-y 14 having layers 141 to 14,, , where layer 14 shadow serves as the buffer layer, (c), a displacement layer 16, (d) an active layer of GaJh i- ⁇ As 18, and (f) a thin capping layer of InAsyPi-y 20.
- the substrate 12 is of known composition and can be obtained from a commercial source.
- the composition y of the InAsyPi-y step-grade 14 is varied incrementally to accommodate the majority of the mismatch.
- the InAsyPi-y buffer layer 14 n is grown to a thickness of about one (1) ⁇ m.
- the intermediate region 16 containing the displacement layer is deposited on the buffer layer.
- the GaJhi-jAs active layer 18 is deposited on the intermediate region.
- the InAsyPj.-y cap 20 is grown to a thickness of about 300 A and provides electrical passivation and carrier confinement.
- MOVPE growth of GaJn ⁇ - ⁇ As/InAsyP ⁇ -y heterostructures was conducted on two-inch (2")
- the orientation of the substrates is 2° off [001] toward [101].
- the samples were inductively heated in purified hydrogen to 620°C with an ambient pressure of 650 torr. All layers were grown without interrupts using a constant trimethylindium flow rate.
- InAsyPi-y was grown with a fixed flow rate of phosphine, with the composition y controlled by varying the arsine flow rate.
- An alternate flow of trimethylgallium is used to grow Ga ⁇ Im. ⁇ As in the 0.5-eV bandgap range at a typical rate of 5-6 ⁇ m/h .
- TEM Transmission electron microscope
- the strain of epitaxial layers was determined using the lattice spacings measured in X-ray diffraction (XRD) ⁇ f2 ⁇ scans of collections of asymmetric and (nearly) symmetric reflections, hi particular, the (h0£) reflections were used, which are oriented in the plane containing the substrate normal and [001].
- the XRD patterns were measured on a Scintag XI powder diffractometer.
- the end-points ⁇ and ⁇ (J - ) are the lattice constants parallel and perpendicular to the substrate plane, respectively, and are determined by linear least-squares fit of a( ⁇ ) with respect to sin 2 ⁇ .
- the equilibrium lattice constant and composition are extracted by relating ⁇ and c ) for a semiconductor alloy film in a biaxial strain field.
- Elastic constants for the alloys are linearly interpolated from the end-point binary compounds.
- a series of samples with approximately fixed Ga x Ini- x As composition was grown to cover a range of buffer compositions.
- the number of steps in the InAsyPi-y grade was varied among the samples, with a nominal misfit increment of 0.20% per step, so that the last step comprised a buffer with the desired composition.
- the step thickness was 0.3 ⁇ m, and the buffer layers were 1 ⁇ m thick.
- XRD XRD provides a quantitative determination of strain, composition, and interfacial coherence, as illustrated in FIG.2.
- the variations in strain of the buffer and active layers are readily apparent as the number of steps and buffer-layer composition are altered (see Table 1 below).
- Table 1 Gah As/InAsP DH composition and structure properties
- the inventors of the present invention have discovered that matching the in-plane lattice constant of the buffer layer to the bulk lattice constant of the active layer can improve the material quality of the active layer. Corresponding improvement in minority-carrier lifetime result from the elimination of misfit dislocations, which act as recombination centers. Minority-carrier lifetime serves as a reliable indicator of device performance, without the need for additional processing.
- the bulk misfit difference acrross the heterointerface between the active layer and the buffer layer is:
- the optimized buffer is one that minimizes the magnitude of the difference between the bulk misfit of the active layer and the in- plane misfit of the buffer layer:
- Table 2 GalnAs/InAsP DH recombination and interface properties.
- the bulk misfit difference in the optimized structure is approximately ⁇ / op t ⁇ uffer •
- the active region should be spatially displaced from the step-grade region to limit the influence of dislocations on the material quality of the active layer.
- Ga m-jAs active layer and cap illustrates continuity of the trend near the optimal condition, as indicated on the graph.
- the composition and structure of this sample are listed in Table 3.
- Table 3 InAsP buffer-layer composition and structure.
- the active layer is capped with a thin, pseudomorphic InAsyPi-y layer.
- step n The final step (step n) of the grade forms the buffer layer, with misfit /buffer and thickness buffer .
- the thickness of the buffer is extended, such that ibuffer ⁇ /istep , to control the degree of strain in the buffer layer, as needed.
- the active layer has bulk misfit /active , and is of arbitrary thickness /lactive • "
- the active layer is unstrained ( acti e ⁇ 0 ) in the optimized structure, with in-plane misfit / act i e ⁇ /active- Strain is eliminated in the active layer by selecting the parameters n, /bu fer and ibuffer such that
- the intermediate region contains a displacement layer that is lattice-matched to the active layer.
- the displacement layer may also contain a number of suitable heterointerfaces designed to limit dislocation propagation into the active region.
- the capping layer is also lattice-matched to the active layer.
- step- ⁇ relaxes during growth of the buffer layer, such that f n -i ⁇ fn- ⁇ - Upon reaching sufficient thickness, the buffer layer partially relaxes to an in-plane mismatch of / b u fer > / «-- ⁇
- the strain in the buffer generally lies in the range - ⁇ / s te ⁇ b uffer ⁇ 0.
- the full utility of the step-grade is realized when the misfit of step n - 1 is less than that of the active layer (i.e., f n - ⁇ ⁇ /active).
- the optimized buffer provides a surface upon which a strain-free active layer can be deposited without misfit dislocations. This condition is desirable for an number of applications that require layers of high material quality.
- the unstrained configuration of the active layer engineered by this invention can, in principle, be maintained to unlimited thickness of the active layer, provided that the strain in the buffer layer remains constant as subsequent layers are deposited.
- this invention can be applied to a variety of mismatched systems by substitution of the relevant substrate and alloy materials and structural specifications.
- the active layer and buffer layer are composed of different alloy systems (such as GaJni-jAs/InAsyPi-y ), dislocation propagation and strain relaxation can be affected by the discontinuity in the elastic properties and growth behavior across the heterointerf ace.
- the film and buffer are composed of different alloy systems, adjustments in the target compositions may be required to compensate for differences in thermal expansion among the constituent alloys.
- the alloy material of the step-graded and intermediate regions may be tailored to accomodate the deposition of a specific lattice-mismatched crystal material on a suitable substrate.
- the intermediate region may incorporate multilayers of appropriate alloy materials in a configuration designed to prevent threading dislocations from reaching the active region.
- the DH structure consists of an InAsyPi-y compositionally step-graded region terminated with a buffer layer, a GaJn ⁇ - ⁇ ;As active layer, and an InAsyPi-y cap.
- Lattice- mismatch introduces biaxial strain, which alters the correct condition for lattice matching the buffer layer to the unstrained active layer.
- the minority-carrier lifetime in these structures is related to the difference between the bulk misfit of the active layer and the in-plane misfit of the strained buffer layer.
- the optimum degree of mismatch in the buffer needed to eliminate strain from the Ga * In 1 ..jcAs active layer generally exceeds the bulk mismatch of the active layer by a fraction of the mismatch increment zd step within the grade.
- the alloy composition of the buffer layer is altered from that of the prior art to acheive the optimized structure. Further improvements of these structure can be realized by incorporating an unstrained, InAsyPi-y displacement layer in the intermediate region between the buffer and active layers.
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AU2002324889A AU2002324889A1 (en) | 2002-09-05 | 2002-09-05 | Method for achieving device-quality, lattice- mismatched, heteroepitaxial active layers |
US10/526,785 US20060048700A1 (en) | 2002-09-05 | 2002-09-05 | Method for achieving device-quality, lattice-mismatched, heteroepitaxial active layers |
PCT/US2002/028314 WO2004022820A1 (en) | 2002-09-05 | 2002-09-05 | Method for achieving device-quality, lattice- mismatched, heteroepitaxial active layers |
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Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2008084488A2 (en) | 2007-01-11 | 2008-07-17 | Red Bend Ltd. | Method and system for in-place updating content stored in a storage device |
US8067687B2 (en) | 2002-05-21 | 2011-11-29 | Alliance For Sustainable Energy, Llc | High-efficiency, monolithic, multi-bandgap, tandem photovoltaic energy converters |
US8173891B2 (en) | 2002-05-21 | 2012-05-08 | Alliance For Sustainable Energy, Llc | Monolithic, multi-bandgap, tandem, ultra-thin, strain-counterbalanced, photovoltaic energy converters with optimal subcell bandgaps |
US8507365B2 (en) | 2009-12-21 | 2013-08-13 | Alliance For Sustainable Energy, Llc | Growth of coincident site lattice matched semiconductor layers and devices on crystalline substrates |
US8575471B2 (en) | 2009-08-31 | 2013-11-05 | Alliance For Sustainable Energy, Llc | Lattice matched semiconductor growth on crystalline metallic substrates |
US8772628B2 (en) | 2004-12-30 | 2014-07-08 | Alliance For Sustainable Energy, Llc | High performance, high bandgap, lattice-mismatched, GaInP solar cells |
US8772623B2 (en) | 2002-05-21 | 2014-07-08 | Alliance For Sustainable Energy, Llc | Low-bandgap, monolithic, multi-bandgap, optoelectronic devices |
US8961687B2 (en) | 2009-08-31 | 2015-02-24 | Alliance For Sustainable Energy, Llc | Lattice matched crystalline substrates for cubic nitride semiconductor growth |
US9041027B2 (en) | 2010-12-01 | 2015-05-26 | Alliance For Sustainable Energy, Llc | Methods of producing free-standing semiconductors using sacrificial buffer layers and recyclable substrates |
US9425249B2 (en) | 2010-12-01 | 2016-08-23 | Alliance For Sustainable Energy, Llc | Coincident site lattice-matched growth of semiconductors on substrates using compliant buffer layers |
US9543468B2 (en) | 2010-10-12 | 2017-01-10 | Alliance For Sustainable Energy, Llc | High bandgap III-V alloys for high efficiency optoelectronics |
US9590131B2 (en) | 2013-03-27 | 2017-03-07 | Alliance For Sustainable Energy, Llc | Systems and methods for advanced ultra-high-performance InP solar cells |
EP3923349A1 (en) | 2018-01-17 | 2021-12-15 | SolAero Technologies Corp. | Four junction solar cell and solar cell assemblies for space applications |
-
2002
- 2002-09-05 AU AU2002324889A patent/AU2002324889A1/en not_active Abandoned
- 2002-09-05 WO PCT/US2002/028314 patent/WO2004022820A1/en not_active Application Discontinuation
Non-Patent Citations (2)
Title |
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CONF. PROC. - INT. CONF. INDIUM PHOSPHIDE RELAT. MATER., 5TH, 1993, pages 135 - 138 * |
DATABASE HCAPLUS [online] KAE-NUNE ET AL.: "Strain relaxation of Ga0.2In0.8As and InAsO.5P0.5 layers grown on InP substrate for 1.6 to 2.4 mum spectral range GaxIn1-xAs/InAsyP10y/InP photodiodes application", XP002959502, accession no. ACS Database accession no. 1994-468986 * |
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US9231135B2 (en) | 2002-05-21 | 2016-01-05 | Alliance For Sustainable Energy, Llc | Low-bandgap, monolithic, multi-bandgap, optoelectronic devices |
US8772623B2 (en) | 2002-05-21 | 2014-07-08 | Alliance For Sustainable Energy, Llc | Low-bandgap, monolithic, multi-bandgap, optoelectronic devices |
US8173891B2 (en) | 2002-05-21 | 2012-05-08 | Alliance For Sustainable Energy, Llc | Monolithic, multi-bandgap, tandem, ultra-thin, strain-counterbalanced, photovoltaic energy converters with optimal subcell bandgaps |
US8067687B2 (en) | 2002-05-21 | 2011-11-29 | Alliance For Sustainable Energy, Llc | High-efficiency, monolithic, multi-bandgap, tandem photovoltaic energy converters |
US9293615B2 (en) | 2002-05-21 | 2016-03-22 | Alliance For Sustainable Energy, Llc | Low-bandgap, monolithic, multi-bandgap, optoelectronic devices |
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US9484480B2 (en) | 2004-12-30 | 2016-11-01 | Alliance For Sustainable Energy, Llc | High performance, high bandgap, lattice-mismatched, GaInP solar cells |
US8772628B2 (en) | 2004-12-30 | 2014-07-08 | Alliance For Sustainable Energy, Llc | High performance, high bandgap, lattice-mismatched, GaInP solar cells |
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US8507365B2 (en) | 2009-12-21 | 2013-08-13 | Alliance For Sustainable Energy, Llc | Growth of coincident site lattice matched semiconductor layers and devices on crystalline substrates |
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US9041027B2 (en) | 2010-12-01 | 2015-05-26 | Alliance For Sustainable Energy, Llc | Methods of producing free-standing semiconductors using sacrificial buffer layers and recyclable substrates |
US9590131B2 (en) | 2013-03-27 | 2017-03-07 | Alliance For Sustainable Energy, Llc | Systems and methods for advanced ultra-high-performance InP solar cells |
US10026856B2 (en) | 2013-03-27 | 2018-07-17 | Alliance For Sustainable Energy, Llc | Systems and methods for advanced ultra-high-performance InP solar cells |
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