Preparation of semi-insulating CdTe by post growth annealing

Thermodynamic conditions for a post growth annealing to prepare near stoichiometric semi-insulating (SI) of CdTe with a minimized concentration of point defects are looked for in undoped and Sn-doped single crystals. The high temperature (200-1000degreesC) in-situ conductivity sigma and Hall effect measurements are used to control the native defect density and to find out the Cd pressure P-Cd at which shallow defects are compensated. We show, that contrary to the undoped samples, where the change of the type of conductivity by variations of P-Cd is easy, the Sn-doped samples exhibit due to the Sn self-compensation much more stable behavior. The temperature near 500degreesC is reported to be optimum for the real-time annealing of bulk samples. The chemical diffusion is sufficiently fast at this temperature, simultaneously the lower temperature is preferred because the native defect density can be tuned gently by changing P-Cd. The measurement of temperature dependencies of sigma in annealed samples below 500degreesC is used to establish the position of Fermi level and to characterize the structure of both shallow and deep levels detected in the sample. The quasichemical formalism is used for evaluation of defect density and for analysis of nature of deep levels.