ALBERT

Notes: Distinct antiphase domain structures in GaAs epitaxial layers grown on a Si/SiO2/Si-substrate structure by metalorganic chemical vapor deposition have been revealed by using a silicon etchant (HF/HNO3). The antiphase is characterized by the [011]-oriented etching textures which rotate 90° between adjacent domains. The corresponding lattice rotation is further confirmed by a convergent beam electron diffraction technique. The size of the antiphase domains is found to increase with increasing film thickness and to grow upon annealing at temperatures above 700 °C. The maximum size of the domain, however, is found to be limited by the film thickness. The majority of the domain boundary lines revealed by chemical etching on the (100) surface do not correspond to any crystalline orientation. Only small segments are found to orient along [011], [010], [021], and, occasionally, [031] and [041] directions. Cross-sectional transmission electron microscopy studies confirmed that the boundaries are generally in curved configurations or zigzag configurations constituted of (011), (010), and (121) planes. All the boundaries are initiated at the interface and propagate through the film in the growth direction. Diffraction contrast experiments show a stacking-faultlike contrast of intrinsic type, indicating an inward relaxation of the lattice planes at the boundary. The rapid chemical reaction of the boundary with the silicon etchant, the intrinsic nature of the lattice distortion at the boundary, and the curved configuration of the boundary indicate that the boundary atoms are replaced by Si atoms. The higher concentration of Si atoms at the antiphase boundary has further been verified by energy dispersive x-ray analysis. In view of the reduction of bond distortion energy, the segregation of Si atoms at the antiphase boundary eliminates the highly distorted GaGa and AsAs bonds and is, therefore, an energetically favorable process. The possible antiphase boundary structure and a mechanism for its migration are discussed. Spatially resolved photoluminescence and cathodoluminescence studies reveal that both the antiphase boundaries and the defective interfacial regions contain nonradiative recombination centers. The luminescence efficiency of the domains increases strongly after annealing.

Notes: The minority-carrier lifetime has been measured by time-resolved photoluminescence in epitaxial films of GaAs grown by metalorganic chemical vapor deposition. The measured lifetimes in thicker devices are 4 to 6 times the theoretical or radiative lifetime. These long lifetimes are the result of photon recycling or self-generation of the self-absorbed radiation.

Notes: Lifetimes at Ga1−xInxP/GaAs heterojunction interfaces determined by photoluminescence power dependence measurements and diffusion model calculations have been correlated to dislocation densities derived from high-resolution x-ray diffraction measurements. The diffusion model calculations are used to determine lifetimes in the region of misfit dislocations by fitting experimental power dependencies of buried-layer photoluminescence. High-resolution x-ray diffraction reveals dislocation densities through the broadening of diffraction peaks due to slight lattice tilts introduced by the dislocations. Lifetimes and dislocation density per dislocation length are correlated to show the functional relationship between the dislocation density and the density of the lifetime-limiting recombination center at the interface.

Notes: The thickness dependence of material quality of InP-GaAs-Si structures grown by atmospheric pressure metalorganic chemical vapor deposition was investigated. The InP thickness was varied from 1–4 μm, and that of the GaAs from 0.1–4 μm. For a given thickness of InP, its ion channeling yield and x-ray peak width were essentially independent of the GaAs layer thickness. The InP x-ray peak widths were typically 400–440 arcsec for 4-μm-thick layers grown on GaAs. The GaAs x-ray widths in turn varied from 320–1000 arcsec for layer thicknesses from 0.1–4 μm. Cross-sectional transmission electron microscopy showed high defect densities at both the InP-GaAs and GaAs-Si interfaces. In 4-μm-thick InP layers the average threading dislocation density was in the range (3–8)×108 cm−2 with a stacking fault density within the range (0.4–2)×108 cm2. The He+ ion channeling yield near the InP surface was similar to that of bulk InP (χmin∼4%), but rose rapidly toward the InP-GaAs heterointerface where it was typically around 50% for 1-μm-thick InP layers. All samples showed room-temperature luminescence, while at 4.4 K, exciton-related transitions, whose intensity was a function of the InP thickness, were observed.

Notes: We have observed anisotropic behavior of the polarization of low-temperature photoluminescence from thick gallium arsenide grown on silicon substrates. The identification of the observed transitions was obtained from analysis of the selection rules, the temperature dependence of the feature intensities, and the transition energies. We find that the low-temperature doublet peaks are due to the emissions from two regions of material experiencing two different kinds of stress, one being biaxial and the other uniaxial. The anisotropy is due to the preferential direction created by parallel microcracks.

Notes: The electrical and structural properties of GaAs layers grown directly by metalorganic chemical vapor deposition on Si substrates oriented 2° off (100) toward [011] are reported. The uniformity of minority-carrier lifetime in the 2 in.- diam heteroepitaxial wafers is comparable to that in bulk GaAs of the same doping density (2×1016 cm−3). Selective etching of the GaAs layer reveals an etch pit density of ∼108 cm−2, consistent with plan view transmission electron microscopy which shows a defect density of ∼108 cm−2. Rapid annealing at 900 °C for 10 s does not significantly alter the heterointerface abruptness, and at the same time the crystalline quality of the GaAs improves slightly. The deep level concentration in the as-grown layer is ∼1013 cm−3 as determined by capacitance spectroscopy. Finally, the activation characteristics of low dose Si implants (3×1012 cm−2 at 60 keV) are similar to those in high quality bulk GaAs.

Notes: The evolution with increasing layer thickness of the structural and electrical properties of GaAs grown directly on Si or Si-on-insulator (SOI) by metalorganic chemical vapor deposition is reported. There is a substantial improvement in the surface morphology and near-surface crystallinity of the GaAs in thicker films (≥1.5 μm). The implant activation efficiency of 60-keV 29Si ions at a thickness of 4 μm is comparable to that seen in bulk GaAs. The deep level concentration is also observed to decrease with increasing layer thickness. Transmission electron microscopy reveals average defect densities near 108 cm−2 in films deposited either on misoriented or exact (100) Si, and in those grown on SOI.

Notes: A series of devices with the structure GaAs/GaAs1−xNx/GaAs and 0.01〈x〈0.03 have been grown by metalorganic chemical vapor deposition. The transient photoconductive decay of these structures is measured as a function of excitation wavelength and injection level. The decay process is generally described by a stretched exponential function with anomously large decay times. The photoconductive excitation spectrum extends into the infrared, well beyond the bandgap of the given alloy. The processes here can be explained by nitrogen clusters that produce charge separation. © 2000 American Institute of Physics.

Notes: InP solar cells were fabricated from films deposited by metalorganic chemical vapor deposition on Si substrates (using a GaAs buffer layer) and on GaAs substrates. Air mass zero efficiencies of 7.1% and 9.4%, respectively, were achieved. Prospects are good for improving the material quality of the InP films, but more work is needed to make the n+-p-p+ structure of the InP solar cells compatible with the silicon substrates, which cause n-type doping of the III-V films.

Notes: The minority-carrier lifetimes of the heteroepitaxial system of GaAs on Si are limited by recombination at mismatch dislocations. Here we show that increasing the thickness of the buffer layer, with an additional annealing step, reduces the dislocation density by about an order of magnitude. At the same time, the minority-carrier lifetime in these double heterostructures increases more than an order of magnitude.