Elastic stiffness, acoustic absorption, and photoelastic constants of the crystal have been determined at room temperature using ultrasonic light diffraction and pulse-echo methods. Two acoustic modes have been found to be particularly useful to acousto-optical applications: One is the shear mode propagated in the [110] direction with displacement along [1̄10], which is characterized by a remarkably high acousto-optical figure of merit, M (n6p2/ρv3) = 793×10−18 sec3/g; and the other is the longitudinal mode along [001] with high figure of merit defined taking account of frequency bandwidth, M′ (n7p2/ρv) = 142×10−7 cm2·sec/g, and low acoustic loss.

All of the elastic stiffness constants except c13 have been found to decrease almost linearly with temperature between −120° and 120°C. The constant c13 reaches the maximum in the vicinity of 0°C, above which it also decreases with temperature. On the other hand, the effective elastic constant (c11–c12)/2, which corresponds to the exceptionally slow shear wave propagating along [110], increases with temperature. The shear wave propagating in the (001) plane making angle of 35.9° with the X axis has zero temperature coefficient of velocity. Acoustic absorptions for several sound modes vary within 1 dB/cm for both the longitudinal wave (measured at 36 MHz) and shear wave (48 MHz) in the measured temperature range. Both real and imaginary parts of the dielectric constants increase monotonically with temperature, while the piezoelectric constant d14 decreases in the temperature range between −150° and 180°C.

The etch-pit density of epitaxial GaAs layers grown on Si was significantly reduced by using the technique of growth interrupt and thermal cycles (in situ TC) followed by growth of In0.1Ga0.9As/GaAs strained-layer superlattices (SLS's). The etch-pit density of 1.4×106 cm-2 (density of small pits by molten KOH etching) was achieved in 3.5 µm-thick GaAs epilayers. It was also found that the effect of SLS's on dislocation reduction was more enhanced by combining with the in situ TC process than the effect when SLS's were used by themselves.

Acoustic phase velocity surfaces and ray directions in paratellurite, TeO2, have been calculated. Characteristic features of the wave propagation in this highly anisotropic medium have been optically confirmed using the shadow method and Schaefer-Bergmann diffraction technique. A small misalignment of the wave normal direction has been found to degrade seriously the performance characteristics of acoustic or acousto-optical devices composed of a highly anisotropic medium such as TeO2. The existence of the transverse mode with a zero temperature coefficient of velocity has been also confirmed by the present calculation and experiment.

Epitaxial growth using thermal annealing and a strained layer superlattice is studied to obtain high-quality GaAs device layers on Si substrates. Crystalline quality of GaAs-on-Si is found to improve with thermal cyclic annealing at temperatures higher than the growth temperature and cooling down to 300°C. It is also found that the optimum InGaAs/GaAs strained layer superlattice buffer structure is one whose total thickness is several times the calculated critical thickness for the average In-mole fraction of the SLS buffer. Configurations and structures of dislocation reductions are ex-amined by TEM observations. A GaAs solar cell is successfully constructed and is found to show total area efficiencies of 18.3% under AM 0 and 20.0% under AM 1.5 conditions.