Samples of In-doped material were investigated by using admittance spectroscopic and photoluminescence methods. It was found that 2 acceptor traps were introduced by In doping. One of these was the well-known A-center at Ev+0.15eV, and the other was located at Ev+0.27eV. The latter was suggested to play a pivotal role in producing a sudden change in conductivity as a critical composition.

K.Suzuki, K.Inagaki, S.Seto, I.Tsubono, N.Kimura, T.Sawada, K.Imai: Journal of Crystal Growth, 1996, 159, 388-91