Changes in the Electrical Parameters of CdTe-based Crystals During Isothermal Annealing

We observed a novel unanticipated effect in CdTe, Cd_1-xZn_xTe and Cd_1-xMn_xTe crystals whilst we were measuring the dependences of several electrical properties (e.g., specific conductivity and free-carrier density) over time. During isothermal annealing under constant thermodynamic conditions (temperatures of 450- 500^° C and under maximal cadmium-vapor pressure), we recorded a jump-like increase in the conductivity after some ~ 1 - 2 hours of heating required to stabilize the sample´s electric parameters. The values of specific conductivity and free-carrier density suddenly increased by up to tenfold, and they persisted at those levels during further ageing. At the same time, the sample´s conductivity became insensitive to stoichiometric changes in the crystal. We explain this effect as reflecting a sudden reformatting of the sample´s native/foreign point-defect structure. This transformation is evaluated and mathematically approximated within the framework of our model of the melting of Te-containing second-phase particles; this process releases impurities from within the particles. The respective diffusion “clouds” grow, and at the moment of their mutual percolation (infiltration), a peculiar “short circuit” is observed with striking changes in the crystals´ electrical parameters.