Monocrystals that were co-doped with Te and S were studied by using capacitance transient methods. The Te doping gave rise to a free carrier concentration that was about 10 times greater than that given by the S content. This produced conditions that were suitable for the measurement of the S-related deep donor (DX-like level). The emission and capture barriers were determined. The value of the former was found to be different from that measured in S-doped samples. The shape of the transients could be described by a Gaussian broadening of the barrier energy. The emission transients were found to be almost exponential, with a Gaussian broadening energy of less than 0.005eV, while the capture process was strongly non-exponential; with an energy of 0.025 to 0.030eV. The non-exponentiality was explained in terms of a spatial variation of the capture barrier; due to a fluctuating potential of the shallow charged impurities.

P.Hubík, J.J.Mareš, J.Krištofik, V.Sestáková, B.Stepánek: Semiconductor Science and Technology, 1996, 11[7], 989-95