Deep-level transient spectroscopy was used to study defect states in crystals of n-type material which had been subjected to various annealing treatments. By comparing Bridgman and travelling-heater crystals, it was deduced that the electrical properties were markedly affected by residual impurities. Eleven defect states were found, which had activation energies that ranged from 0.2 to 0.86eV. One of these defect states was found only in In-doped samples. At least 3 of them were related to residual impurities and could be removed by annealing in liquid Cd. Some of the defects were suggested to be complex centers that involved native defects and impurities.

G.M.Khattak, C.G.Scott: Journal of Physics - Condensed Matter, 1991, 3[44], 8619-34