Abstract
Photoluminescence and photoacoustic spectroscopy were used to investigate die effect of post-growth annealing carried out to improve the uniformity of Czochralski-grown semi-insulating GaAs. Single- and multi-step, ingot- and wafer-annealed crystals were studied. It is shown that wafer-annealed crystals do not present the additional defect-related transitions found in ingot-annealed samples. One of these defects is concluded to originate from arsenic precipitates. A second additional band is asserted to originate from an acceptor-like defect with a binding energy of 69 meV. Besides the improvement in crystalline quality, it is shown that the residual impurities, silicon and zinc, occur in very low concentrations in wafer-annealed samples, probably owing to an out-diffusion process during the thermal treatments.