Effect of Heat Treatment on Gallium Arsenide Crystals II. Properties of Crystals Heat-Treated in Chalcogen Vapor

Abstract

Melt-grown n-GaAs crystals were heat-treated in a sulfur vapor or a mixed vapor of sulfur and arsenic, and their electrical properties were investigated. The chalcogen vapor appeared to suppress thermal conversion of crystal from n-type to p-type conductivity. The crystals showed two donor levels with ionization energies of nearly 0.15 eV and 0.002 eV, respectively. Concentration of the 0.15 eV deep donor was lower for the samples heat-treated at higher temperatures and in a vapor of lower sulfur content, and tended to decrease with increase in acceptor concentration. The deep donor was thus attributed to a complex center, including arsenic vacancies, and its dissociation energy was estimated to be nearly 1.5 eV. The product of the concentration and the scattering cross section of space-charge region, N _s A, was found to increase in proportion to acceptor concentration. This fact indicates that the space-charge region arises where shallow donors are strongly compensated for with acceptors.