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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

In Situ MOVPE Smoothing of Acoustically Spalled GaAs for Substrate Reuse

High material costs, especially for substrates, have limited the widespread adoption of III-V photovoltaics. A potential to reduce this cost is to reuse the III-V substrate via acoustic spalling, however this technique can leave a rough surface, hindering subsequent device performance. This research investigates the potential of using metalorganic vapor-phase epitaxy growth as a buffer layer to smooth the surface of acoustically spalled germanium and gallium arsenide (GaAs) substrates for improved III-V photovoltaic cell yield and performance, while retaining the maximum number of reuses of a substrate. Three potential smoothing layers were explored: lightly doped C:GaAs, highly doped Se:GaInP, and lightly doped Se:GaInP. C:GaAs showed the most promise as a smoothing layer, while Se:GaInP tended to conform to the underlying morphology, potentially increasing roughness in some areas. Utilizing 5 ..mu..m of C:GaAs as a planarizing buffer increased the average efficiency (without an antireflection coating) from an as-spalled baseline from 2.1% to 4.9% and performing a 5-min 30 degrees C 8:1:1 H2SO4:H2O2:H2O etch prior to a 5 ..mu..m of C:GaAs as a planarizing buffer further increased efficiency to 11.1%.

14 SOLAR ENERGY↗
DOE OSTI2021

(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics

We demonstrate the growth of (110) GaAs solar cells by hydride vapor phase epitaxy (HVPE) as an advance towards a (110)-oriented device platform with substrate reuse via spalling. Controlled spalling offers a fracture-based path to substrate amortization, allowing device removal and substrate reuse, but the faceted surface generated in spalling of (100)-GaAs presents hurdles to direct regrowth of subsequent devices. Spalling of (110)-oriented substrates takes advantage of the natural (110) cleavage plane in zinc-blende III-V materials, eliminating this faceting. The vast majority of III-V epitaxy development is on (100)-oriented substrates, but epitaxy is not limited to this orientation. Here, we demonstrate (110)-based GaAs solar cells grown by HVPE with equivalent performance to devices grown on the more standard (100) orientation. We also demonstrate spalling of (110) oriented substrates, revealing surfaces with flat terraces separated by steps. These results provide preliminary evidence of a potentially low-cost path for terrestrial III-V photovoltaics via the (110) substrate orientation.

(110) orientation↗
DOE OSTI2021

Improving GaAsP/Si Tandem Solar Cells Using Silicon Passivated Contacts

The degradation of photocarrier bulk lifetime in Si wafer substrates during the heteroepitaxial growth of III-V materials has been widely reported and is known to limit the efficiency of III-V/Si tandem solar cells. There have been prior strategies to protect Si lifetime in III-V growth chambers, but most require the use of a protective layer that must be removed in subsequent device processing. It would be advantageous for protective layers to remain an active part of the device. In this work, we demonstrate that a polycrystalline silicon (poly-Si) passivated contact can protect the minority carrier lifetime of the Si base wafer during the organometallic vapor phase epitaxy of III-V materials on silicon substrates.

Exascale Computing Project↗
DOE OSTI2021

Demonstration of Passivation Using a Low-Temperature-Grown, Al-Containing Window Layer by HVPE

We present hydride vapor phase epitaxy (HVPE) growth of single junction GaAs solar cells with Al0.4Ga0.6As front passivation layers at a growth temperature of 650°C. Devices achieved a short circuit current density of ~27.52 mA/cm2 after anti-reflection coating, similar to devices that used GaInP windows with the same bandgap, indicating that AlGaAs provides front-surface passivation resulting in a low interface recombination velocity. The low temperature growth of Al containing III-V materials by HVPE allows for compatibility with In-containing alloys in high-efficiency III-V device structures for various applications.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2021

Improved Contacts for Tandem Cells with Enhanced Effciency Grown by D-HVPE

Dynamic hydride vapor phase epitaxy (D-HVPE) has provided a potential route towards lower cost material growth of III-V photovoltaic devices. A highly doped Ga0.5In0.5P emitter layer is grown in attempt to force passivation at the front of the cell to account for the absence of a suitable window layer in our reactor. Control over dopant diffusion in these materials is thus critical to achieving high-efficiency device performance. Here, we institute a two-step contact layer design that boosts tandem cell efficiencies by minimizing Se diffusion into the underlying emitter layer while still providing sufficiently low contact resistance. Short-circuit current in these devices improves to 8.9 mA/cm2 in an uncoated GaInP/GaAs cell, an improvement of 1.2 mA/cm2 over our previous best cell. Conversion efficiency with the new contact doping scheme is projected to be ~27% with the inclusion of a standard ARC layer.

27 ARPA - Advanced Research Projects Agency-Energy↗
DOE OSTI2024

Planarizing Spalled GaAs(100) Surfaces by MOVPE Growth

III-V photovoltaic devices have demonstrated remarkable performance in many applications, and spalling is a promising technique for reducing device costs by recovering the substrate for reuse. In this study, we investigate the in situ planarization of A-directionally spalled GaAs(100) substrates using metal-organic vapor phase epitaxy (MOVPE) grown C:GaAs with CCl4 as the carbon source. We have characterized the (100)-oriented growth for various CCl4 flow rates and observed that the CCl4 or its by-products promote material diffusion from the facet tops to the underlying valleys. For facets with a height of 5 ..mu..m on a substrate with an A-spall and 6 degreesB -offcut, it took 7 ..mu..m of C:GaAs to planarize the substrate. For a similar sample, with a 6 degreesA -offcut, it required 2 ..mu..m of growth to fill the valleys but there were remnant facets.

III-V↗
DOE OSTI2020

A study on the impact of mid-gap defects on vertical GaN diodes

GaN is a favorable martial for future efficient high voltage power switches. GaN has not dominated the power electronics market due to immature substrate, homoepitaxial growth, and immature processing technology. Understanding the impact of the substrate and homoepitaxial growth on the device performance is crucial for boosting the performance of GaN. Here, we studied vertical GaN PiN diodes that were fabricated on non-homogenous Hydride Vapor Phase Epitaxy (HVPE) substrates from two different vendors. We show that defects which stemmed from growth techniques manifest themselves as leakage hubs. Different non-homogenous substrates showed different distribution of those defects spatially with the lesser quality substrates clustering those defects in clusters that causes pre-mature breakdown. Energetically these defects are mostly mid-gap around 1.8Ev with light emission spans from 450nm to 700nm. Photon emission spectrometry and hyperspectral electroluminescence were used to locate these defects spatially and energetically.

42 ENGINEERING↗
NASA NTRS1972

Development of high temperature gallium phosphide rectifiers

Large area high performance, GaP rectifiers were fabricated by means of Zn diffusion into vapor phase epitaxial GaP. Devices with an active area of 0.01 sq cm typically exhibit forward voltages of 3 volts for a bias current of 1 ampere and have reverse breakdown voltages of 300 volts for temperatures from 27 C to 400 C. Typical device reverse saturation current at a reverse bias of 150 volts is less than 10 to the minus 9th power amp at 27 C and less than 0.000050 amp at 400 C.

Craford, M. G.↗
NASA NTRS1973

Vapor phase growth of group 3, 4, and 5 compounds by HCl transport of elements

Technique has been devised for vapor-phase epitaxial growth of group 3, 4, and 5 binary, ternary, or quaternary compounds by HCl transport of the constituent elements or dopants. Technique uses all the constituents of the alloy system in their elemental form. Transport of these elements by an HCl + H2 carrier gas facilitates their transport as subchlorides.

Tyagi, R. C.↗
NASA NTRS1975

Low cost AMOS solar cell development

Recent developments at JPL have demonstrated that high conversion efficiencies are found with GaAs metal semiconductor solar cells when a particular heat treatment processing step is used to introduce an interfacial layer between the metal and the semiconductor. The new cell, called AMOS (Antireflection-Coated Metal-Oxide-Semiconductor), has open circuit voltages of 0.68-0.72 volts and efficiencies of 15% under terrestrial sunlight, as compared to values of 0.45-0.48 volts and 10%, respectively, for similar cells without an interfacial layer. Potentially higher efficiencies are feasible as further improvements are made in optimizing the interfacial layer effect and in increasing the blue response of the cells. A thin film AMOS cell is proposed that uses a thin recrystallized germanium (Ge) layer between a low cost metal substrate and the vapor phase epitaxially (VPE)-grown GaAs.

Stirn, R. J.↗
NASA NTRS1980

The 3-5 semiconductor solid solution single crystal growth

Techniques used for liquid and vapor phase epitaxy of gallium indium arsenide are described and the difficulties encountered are examined. Results show that the growth of bulk III-V solid solution single crystals in a low gravity environment will not have a major technological impact. The float zone technique in a low gravity environment is demonstrated using cadmium telluride. It is shown that this approach can result in the synthesis of a class of semiconductors that can not be grown in normal gravity because of growth problems rooted in the nature of their phase diagrams.

Gertner, E. R.↗
NASA NTRS1982

Progress toward cascade cells made by OM-VPE

Organometallic Vapor Phase Epitaxy (COM-VPE) was used to make a sophisticated monolithic cascade cell, with a peak AMO efficiency of 16.6%, not corrected for 14% grid coverage. The cell has 9 epitaxial layers. The top cell is 1.35 microns thick with a 0.1 micron thich emitter. Both cells are heteroface n-p structures. The cascade cell uses metal interconnects. Details of growth and processing are described.

Borden, P. G.↗
NASA NTRS1982

Radiation damage and annealing in large area n+/p/p+ GaAs shallow homojunction solar cells

Annealing of radiation damage was observed for the first time in VPE-grown, 2- by 2-cm, n+/p/p+ GaAs shallow homojunction solar cells. Electrical performance of several cells was determined as a function of 1-MeV electron fluence in the range of 10 to the 13th power to 10 to the 15th power e-/sq cm and as a function of thermal annealing time at various temperatures. Degradation of normalized power output after a fluence of 10 to the 15th power 1-MeV electrons/sq cm ranged from a low of 24 to 31 percent of initial maximum power. Normalized short circuit current degradation was limited to the range from 10 to 19 percent of preirradiated values. Thermal annealing was carried out in a flowing nitrogen gas ambient, with annealing temperatures spanning the range from 125 to 200 C. Substantial recovery of short circuit current was observed at temperatures as low as 175 C. In one case improvement by as much as 10 percent of the postirradiated value was observed. The key features of these cells are their extremely thin emitter layers (approxmately 0.05 micrometers), the absence of any Al sub xGd sub 1-x As passivating window layer, and their fabrication by vapor phase epitaxy.

Flood, D. J.↗
NASA NTRS1988

Development program for 1.93-micron lasers

For the first time lasers operating at 1.93 microns were demonstrated. The lasers were fabricated by Vapor Phase Epitaxial (VPE) growth techniques currently used for the fabrication of high power lasers at 1.3 microns. The structure of these laser diodes consisted of compositionally graded, sulfur-doped InAsP, grown on an InP substrate; a constant-composition n+InAs(0.27)P(0.73) layer, which is the first cladding layer; an In(0.66)Ga(0.34)As layer, which is the active region, and a second InAs(0.27)P(0.73) layer. The devices were oxide-stripe DH lasers (gain-guided only). The best devices had 80 K lasing thresholds in the range of from 80 to 150 mA, and T sub o (below 220 K) in the range of 60 to 90 K. The highest observed temperature of oscillation was 15.5 C. The highest observed power output at 80 K was in the range of 3 to 5 mW. The calculated delta I/delta T was 4.4 A/K. As a part of the materials development, PIN homojunction detectors having the band edge near 1.93 were also fabricated. The best devices (100 micron diameter, mesa structure) exhibited room temperature dark currents in the range of from 20 to 50 nA and had QE at 1.93 microns in the range of 35 to 40 percent. In addition to the device results, the InGaAs-InAsP materials system was extensively investigated and low defect density layers can now be grown allowing for significant device performance improvement.

Longeway, P.↗
NASA NTRS1987

Development of a unique laboratory standard: Indium gallium arsenide detector for the 500-1700 nm spectral region

A planar (5 mm diameter) indium gallium arsenide detector having a high (greater than 50 pct) quantum efficiency from the visible into the infrared spectrum (500 to 1700 nm) was fabricated. Quantum efficiencies as high as 37 pct at 510 nm, 58 pct at 820 nm and 62 pct at 1300 nm and 1550 nm were measured. A planar InP/InGaAs detector structure was also fabricated using vapor phase epitaxy to grow device structures with 0, 0.2, 0.4 and 0.6 micrometer thick InP caps. Quantum efficiency was studied as a function of cap thickness. Conventional detector structures were also used by completely etching off the InP cap after zinc diffusion. Calibrated quantum efficiencies were measured. Best results were obtained with devices whose caps were completely removed by etching. Certain problems still remain with these detectors including non-uniform shunt resistance, reproducibility, contact resistance and narrow band anti-reflection coatings.

Source record↗
NASA NTRS1990

Peeled film GaAs solar cells for space power

Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg.

Wilt, D. M.↗
NASA NTRS1988

Hybrid solar cells based on dc magnetron sputtered films of n-ITO on APMOVPE grown p-InP

Hybrid indium-tin-oxide (ITO)/InP solar cells are discussed. The cells are constructed by dc magnetron sputter deposition of ITO onto high-quality InP films grown by atmospheric pressure metal-organic vapor-phase epitaxy (APMOVPE). A record efficiency of 18.9 percent, measured under standard Solar Energy Research Institute reporting conditions, has been obtained. The p-InP surface is shown to be type converted, principally by the ITO, but with the extent of conversion being modified by the nature of the sputtering gas. The deposition process, in itself, is not responsible for the type conversion. Dark currents have been suppressed by more than three orders of magnitude by the addition of hydrogen to the sputtering gas during deposition of a thin (5 nm) interface layer. Without this layer, and using only the more usual argon/oxygen mixture, the devices had poorer efficiencies and were unstable. A discussion of associated quantum efficiencies and capacitance/voltage measurements is also presented from which it is concluded that further improvements in efficiency will result from better control over the type-conversion process.

Coutts, T. J.↗