Photoluminescence Study of Thermal Conversion in GaAs Grown from Silica Boats

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Abstract
GaAs crystals grown from the melt in silica boats without intentionally doping exhibit n‐type conductivity. Photoluminescence measurements at 20°K are used here to study thermal conversion in these crystals. Heat treatments with temperature TH ranging from 600° to 1100°C followed by quenching were performed on three crystals with different carrier concentrations. For TH≥900°C, it is concluded that the thermal conversion in quenched crystals is caused both by copper acceptors and by the shallow acceptors which are responsible for the 1.49 eV emission band in the original crystals. The latter acceptors are suggested to be silicon. It is proposed that conversion associated with silicon results from transfer of silicon atoms from donor sites to acceptor sites through a trapping process during rapid quenching. The maximum compensation due to these shallow acceptors is estimated, depending on the crystal used, to be on the order of 5×1016 cm−3 at 1100°C and is smaller at lower temperatures. For TH≤870°C, it appears that copper is solely responsible for the conversion.