STOICHIOMETRY-DEPENDENT NATIVE ACCEPTOR AND DONOR LEVELS IN GA-RICH-N-TYPE GALLIUM-ARSENIDE

By combining photoluminescence and optical deep-level transient spectroscopy measurements, we have investigated the presence of a native acceptor level H01 situated at 0.32 eV above the valence band, in n-type Si-doped liquid-encapsulated Czochralski GaAs grown in stoichiometric and Ga-rich conditions. The concentration of H01 decreases when increasing the [Ga]/[As] ratio up to a critical threshold of 1.3. For [Ga]/[As] ratio greater than 1.3, H01 disappears and another acceptor level, H02 (E(upsilon) + 0.23 eV), is detected. H02 is identified as the double-acceptor level of the gallium antisite Ga(As). Photoluminescence results show the presence of a high-intensity 1-eV band which disappears for [Ga]/[As] ratios greater than 1.2. The annihilation of this band is accompanied by the appearance of two emission bands centered at 0.95 and 1.2 eV. The dependence of the free-carrier concentration on the presence of H01 is interpreted in terms of a complex defect formed by a gallium vacancy and silicon impurity which can be the possible origin of this defect. Finally, the evolution of native electron traps present in these samples, with [Ga]/[As] ratio, is also interpreted to give more information about the origin of the EL6 center in GaAs.