Evaluation of photoelectrical properties of Bi doped CdTe crystals

摘要

Nonequilibrium carrier generation, transport, and recombination features have been investigated in Bi-doped and Yb-codoped bulk CdTe crystals, using time-resolved picosecond free-carrier and photorefractive grating techniques. Peculiarities of deep-impurity dependent carrier generation were studied at below band-gap photo-excitation using 1064 nm wavelength. Carrier transport in light created space charge field provided the instantaneous diffusion coefficient values, dependent on excitation energy, and revealed a sign of the dominant photoexcited carriers in the crystals. The studies provided also a deeper insight into an initial occupation of deep impurity levels, which was found strongly dependent on doping and co-doping. At low Bi density (～2 × 10~(17) cm~(-3)), the hole generation was dominant, while at higher doping (8 × 10~(17) cm~(-3)) the bipolar plasma generation prevailed. Codoping by Yb (～5 × 10~(17) cm~(-3)) revealed deep donor features of deep defects and formation of a strong space charge field. Carrier dynamics in the given crystals wasrncompared with CdTe:V ones, where vanadium is known to form the mid-gap donor levels.