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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.

( GaAs ) 1−x ( Ge 2 ) x alloy layers, 0<x<0.22, have been grown by metal–organic vapor-phase epitaxy on vicinal (001) GaAs substrates. Transmission electron microscopy revealed pronounced phase separation in these layers, resulting in regions of GaAs-rich zinc-blende and Ge-rich diamond cubic material that appears to lead to substantial band-gap narrowing. For x=0.1 layers, the phase-separated microstructure consisted of intersecting sheets of Ge-rich material on {115}B planes surrounding cells of GaAs-rich material, with little evidence of antiphase boundaries. Atomic force microscopy revealed {115}B surface faceting associated with the phase separation.

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.

The strain-induced splitting of the heavy-hole (hh) and light-hole (lh) valence bands for 4-pmthick GaAs/Si is examined on a microscopic scale using linear polarized-cathodoluminescence imaging and spectroscopy. The energies and intensities of the hh-and lh-exciton luminescence are quantitatively analyzed to determine spatial variations in the stress tensor. The results indicate that regions near and far from the microcracks are primarily subject to uniaxial and biaxial tensile stresses, respectively. The transition region where biaxial stress gradually converts to uniaxial stress is analyzed, and reveals a mixing of lh and hh characters in the strain-split bands.In the past decade, improvements in epitaxial-growth techniques have made feasible the hybridization of GaAs and Si technologies for applications of high-speed electronic and optoelectronic devices, despite the 4. 1% lattice mismatch.The ratio of the GaAs and Si thermalexpansion coeScients is about 2.5 at typical growth temperatures in excess of 700 C, and the subsequent cooling to room temperatures results in a large tetragonal distortion which can cause wafer bowing and the formation of microcracks to relieve partially the thermal stress. The effects of stress on the splitting of the j = 2 heavy-hole (hh; m~= + -' , ) and light-hole (lh; m1 =+ -, ' ) bands at k=0 have been previously studied by several authors using photoluminescence (PL), ' photoluminescence excitation (PLE), ' ' cathodoluminescence (CL), ' and photoreflectance (PR);"' optical transitions involving these states exhibit polarization selection rules which depend on the strain. 'In this paper, we present the results of a novel approach in which linearly polarized CL scanning electron microscopy (SEM) is used to analyze spatial variations in the stress tensor for GaAs/Si. Yacobi and co-workers, ' using CL, have demonstrated the presence of local variations in the luminescence near microcracks caused by variations in stress. With the enhancement of a linear-polarizationdetection scheme, we demonstrate that a quantification of the exciton luminescence intensities and energies in the CL spectra can be performed; this leads to a definitive evaluation of the micrometer-scale spatial variations of the hh and lh characters in the strain-split valence bands. The present approach, in conjunction with polarization selection rules which depend on the form of the stress tensor, enables a determination of the spatial distribution of the stress. Scanning monochromatic CL images are presented and reveal a polarization anisotropy within the sample. From the results, we show that the stress is predominantly uniaxial along the microcracks and predominantly biaxial in the regions between the cracks.The samples examined in this study were grown by atmospheric-pressure metal-organic chemical-vapor deposition (MOCVD) at the Spire Corporation. ' A threestep method was used to grow the sample and is described here: the Si substrate [oriented 2' oA' (001) in the (110) direction] was heated in hydrogen to over 100...