Photo-capacitance, deep-level photoluminescence and Hall effect measurements were made of liquid-phase epitaxially grown n-type Ga0.7Al0.3As crystals, after annealing (900C, 1h) under a controlled As vapor pressure. The photo-capacitance measurements revealed the presence of a predominant deep level at Ec-0.5eV. This level density increased with increasing As vapor pressure during annealing. Deep-level photoluminescence bands were also detected at about 1.21 and 1.36eV at 77K, and the photoluminescence band intensity increased with increasing As vapor pressure and Te impurity content. The origin of native defects was considered in terms of deviations from the stoichiometric composition of the ternary alloy system. It was concluded that, in Te-doped samples, the predominant deep levels (DX centers) were affected by the stoichiometry of the crystals, and that the deep levels were associated with the donor impurity, Te, and with excess As.

A.Murai, J.Nishizawa, Y.Oyama, K.Suto, N.Chubachi: Journal of Applied Physics, 1996, 79[8], 3930-4