Photo-capacitance methods were used to investigate stoichiometry-dependent deep levels in p-type Zn-doped crystals that had been annealed (4h, 700C) under controlled P vapor pressures. The results revealed the presence of 3 predominant deep levels. A deep level at 1.05eV above the valence band was usually detected before and after annealing, and changes in level densities were shown to be a function of the P vapor pressure. Another 2 deep levels were also detected, after annealing, at 0.74eV above the valence band and at 0.51eV below the conduction band. The 1.05eV level was considered to be due to a complex defect which was related to impurity-intrinsic defects. The 0.74eV level was formed by annealing under a low P vapor pressure and was attributed to P vacancies that arose due to deviations from stoichiometry. It was concluded that the ionized version of the neutral 1.08eV level was located at 0.51eV below the conduction band.

J.Nishizawa, K.Kim, Y.Oyama, K.Suto: Journal of Applied Physics, 1997, 81[7], 3151-4