Low temperature photoluminescence results from MOCVD epitaxial InP grown on GaAs/Si substrates are presented as a function of thickness of the GaAs buffer layer. As a consequence of thermal expansion mismatch of the heterostructure, the InP layer contains residual stress which causes the band gap to shift and splits the valence band degeneracy of the mj = ± 3/2 and the mj = ± 1/2 bands. Both the shifting and splitting phenomena are clearly seen in tite PL results and are shown to depend on the GaAs buffer layer thickness.

Ceramic thermal barrier coatings extend the operating temperature range of actively cooled gas turbine components, therefore increasing thermal efficiency. Performance and lifetime of existing ceram ic coatings are limited by spallation during heating and cooling cycles. Spallation of the ceramic is a function of its microstructure, which is determined by the deposition method. This research is investigating metalorganic chemical vapor deposition (MOCVD) of yttria stabilized zirconia to improve performance and reduce costs relative to electron beam physical vapor deposition. Coatings are deposited in an induction-heated, low-pressure reactor at 10 microns per hour. The coating's composition, structure, and response to the turbine environment will be characterized.

We have demonstrated the formation of arsenic precipitates in GaAs using arsenic implantation and annealing. Electrical measurements show that very high resistivity (surface or buried) GaAs layers can be produced by this method. The arsenic-implanted materials are similar to GaAs:As buffer layers grown by low-temperature molecular beam epitaxy, which are used for eliminating backgating problems in GaAs circuits. Arsenic implantation is a nonepitaxial process which is compatible with current GaAs technology. Formation of insulating GaAs layers by this technique may improve the performance and packing density of GaAs integrated circuits, leading to advanced novel III–V compound-based technologies for high-speed and radiation-hard circuits.

Lattice matched GaInAs/InP Npn heterojunction bipolar transistors (HBTs) have been grown by low pressure metal organic vapour phase epitaxy (MOVPE) and processed with non-selfaligned fabrication techniques. The transistors exhibit a cutoff frequency of 60 GHz and maximum oscillation frequency of 32 GHz which are the highest values reported to date for GaInAs/InP HBTs grown by MOVPE.

This paper reports advances in the development of solar cells made from GaAs‐on‐Si structures prepared by metalorganic chemical vapor deposition (MOCVD). The use of concentrator cells, operating at ∼200 suns, has led to the efficiency achievements of 21.3% (AM1.5D) for a GaAs‐on‐Si solar cell, and 27.6 (AM1.5D) for a homoepitaxial GaAs cell. The development of epitaxial multilayer dielectric mirrors (Bragg reflectors), as back‐surface reflectors in thin‐film GaAs cells, on both Si and GaAs substrates, is shown to lead to modest efficiency increases, over that of conventional designs.

Metalorganic chemical vapor deposition has been used to form Si delta-doped structures of GaAs-AlxGa1-xAs, which have been characterized by mobility and sheet-carrier density measurements. At 20 K, mobility values of up to 300,000 cm2/V-sec, with carrier densities of almost-equal-to 1 x 10(12) cm-2, are reported. The mobility at 77 K is 131,000 cm2/V-sec. The Si delta-doped region has been imaged by cross-sectional transmission electron microscopy, and is seen to have a width of approximately 30 angstrom. Si delta doping in AlxGa1-xAs (x = 0.23) has also resulted in high carrier levels. with an unexplained amphoteric behavior having been observed.

Nanometer scale GaAs quantum well wire (QWW) arrays with lateral dimensions in the range of 10–70 nm and a period of 200 nm have been fabricated in the GaAs/AlGaAs system using X-ray nanolithography patterning and overgrowth by a low pressure metalorganic vapor phase epitaxy (LP-MOVPE) technique. The QWW structures were fabricated by post-growth patterning of a thin GaAs film on a AlGaAs-coated substrate followed by AlGaAs deposition, or by continuous in-situ deposition of a GaAs/AlGaAs QWW structure on a prepatterned GaAs substrate. Although cross-sectional transmission electron microscopy showed no structural defects in either QWW fabrication process, photoluminescence (PL) was only observed in the in-situ-deposited structures. Strong polarization dependence of the PL peak withrespect to wire orientation has been confirmed and evidence of lateral confinement was observed.

The achievement of cell inefficiencies of 21.3% ( approximately 200X, AM1.5D) for a GaAs-on-Si solar cell, and 27.6% ( approximately 200X, AM1.5D) for a GaAs homoepitaxial solar cell is reported. The value of 21.3% represents the highest efficiency reported for a monolithically grown GaAs-on-Si solar cell, while 27.6% is the highest confirmed value for any single-junction solar cell without the use of a prismatic cover. The GaAs-on-Si cell uses GaAs layers, grown by metalorganic chemical vapor deposition (MOCVD), with a defect density of approximately 2*10/sup 7/ cm/sup -2/. High efficiency in the heteroepitaxial cell has been achieved by careful design of the cell layers, taking into account the actual properties of this highly defected material.<>

High quality GaAs films have been deposited on sawtooth-patterned (0.2 μm period) Si substrates by MOCVD. Three inch diameter Si wafers were patterned using a combination of holographic lithography and wet chemical etching. A two-step deposition process was used resulting in planar films with surface morphology comparable to films deposited on unpatterned substrates. The initial low temperature nucleation layer was found to be amorphous and conformed to the patterned Si surface. Rapid thermal annealing and thermal cycle growth resulted in substantial reduction in the threading defect density. The MOCVD growth and characterization of these films and the possible mechanisms responsible for the reduction/elimination of the defects at the GaAs/Si interface are discussed.

GaAs/Ge two-junction tandems up to 23.4% efficient at 9 AM0 suns were made. This efficiency is a record for a monolithic, two-terminal GaAs/Ge tandem cell, and also exceeds the best efficiency reported (23%) for a single-junction GaAs concentrator at 10 AM0 suns. A GaAs top cell was epitaxially grown on GaAs and Ge wafers simultaneously; the GaAs growth forms a bottom cell in the Ge to make a two-junction tandem cell, while the GaAs top cell on the GaAs substrate is a single-junction experimental control. The best GaAs/Ge tandem was three percentage points more efficient than the best control GaAs/GaAs concentrator; the difference is due to the active Ge bottom cell

This paper reports on the effectiveness of selective area epitaxy by conventional MOCVD and atomic layer epitaxy nucleation techniques in improving the quality of GaAs on Si. The GaAs films were deposited through photolithographically patterned openings in the oxide coated Si wafers. Selective epitaxy was found to eliminate wafer warpage, reduce film cracking and reduce the tensile stresses for islands less than 200 μm/side. Complete stress relief has been achieved in 10 μm/side islands after oxide removal. Thermal cycle growth deposition technique has been employed resulting in two orders of magnitude reduction in the dislocation density and excellent surface morphologies. The potential of selective epitaxy, by the above techniques, in improving the quality of the GaAs on Si films is addressed.

Selective area Epitaxy (SE) of high quality GaAs on Si films has been achieved using conventional MOCVD and Atomic Layer Epitaxy (ALE) nucleation techniques. Epitaxial GaAs films were deposited inside windows etch patterned in the oxide coated Si wafers. SE was found to eliminate wafer warpage, reduce film cracking and reduce the tensile stresses for islands less than 200 μm/side. Complete stress relief has been achieved in 10 μm/side islands after oxide removal. Defect reduction techniques have been employed resulting in two orders of magnitude reduction in the dislocation density and excellent surface morphologies. This paper addresses the potential of SE, by the above techniques in improving the quality of the GaAs on Si films.

InP solar cells have been made by metalorganic chemical vapor deposition (MOCVD) with a graded-junction or front-surface-field structure, in which the doping decreases from 3×1019 cm -3 at the surface to 3×1018 cm-3 at the junction. Improvement was observed in the short-wavelength quantum efficiency and in the overall conversion efficiency relative to standard shallow-homojunction cells, indicating that the graded structure improved collection of carriers generated near the surface. A beginning-of-life conversion efficiency of 19.1% AM0 was measured on a 4-cm2 cell. Measurements on similar cells showed an average of 4.7% degradation after irradiation with 1014-cm-2 electrons at 1 MeV

InP solar cells with AM0 conversion efficiencies exceeding 19% have been produced by adapting the cell structure to accommodate a high surface recombination velocity. This is done by placing the junction very close the surface and using a front-surface field structure in which the doping increases from the junction to the front surface. Analysis of the quantum efficiency at short wavelengths of cells as a function of junction depth indicates that the surface recombination velocity is high (>10/sup 6/ cm/s), which disagrees with measurements made by other techniques.< >

Epitaxial InP films have been successfully deposited on GaAs coated silicon wafers with a buried oxide for the first time by MOCVD. The SOI wafers were prepared using the Separation by IMplantation of Oxygen (SIMOX) process. The quality of InP on SIMOX is comparable to the best of InP on Si deposited in the same reactor. Preliminary results on defect reduction techniques such as Thermal Cycle Growth (TCG) show an order of magnitude increase in the photoluminescence intensity and a factor of five reduction in the defect density. TCG has been found more effective than Thermal Cycle Annealing (TCA) in improving the crystalline perfection and optical properties of the deposited films.