Preparation of semi‐insulating CdTe doped with group IV elements by post growth annealing

Abstract

AbstractThermodynamic conditions for post‐growth annealing to prepare near stoichiometric semi‐insulating CdTe are studied for undoped, and Sn and Ge‐doped single crystals. The main aim of the annealing procedure was to obtain high resistive material with the minimal concentration of native and foreign defects. The high temperature (200 – 1000 °C) in‐situ conductivity σ and Hall effect measurements were used to control the native defect density and to determine the Cd pressure pCd at which shallow defects are compensated. It is shown that contrary to the undoped samples in which the change of the type of conductivity by variations of pCd is easy, the Sn‐ and Ge‐doped samples exhibit a much more stable behavior due to the Sn (Ge) selfcompensation. It was found that: the temperatures near 500 °C is optimum for the real‐time annealing of bulk samples, the chemical diffusion is sufficiently fast at these temperatures while the uncontrolled change of defect density distribution during the subsequent cooling process is minimized. The time‐dependent charge measurement technique was used to characterize the room‐temperature specific resistivity distribution in the as‐grown crystals, which indirectly controls the dynamic of solidification process. This allows us to consider the specific resistivity distribution along the growth direction of each crystal in terms of superposition of segregation and self‐compensation phenomena.