Self-compensation limited conductivity in semi-insulating indium-doped Cd0.9Zn0.1Te crystals

Indium-doped Cd_0.9Zn_0.1Te crystals with semi-intrinsic conductivity have been investigated. Temperature dependence of their electrical characteristics shows a number of unconventional peculiarities: the thermal activation energy of conductivity is “anomalously” low (0.60-0.62 eV); the resistivity at elevated temperatures is greater than its intrinsic value for Cd_0.9Zn_0.1Te; the inversion of the conduction from n- to p-type occurs at a temperature slightly above 300 K, etc. The observed features are explained in terms of statistics of electrons and holes in a semiconductor containing a compensation center, whose concentration is much higher than those of uncontrolled (background) impurities and defects. Comparison of the calculation results and experimental data leads to the conclusion that the donor level, which is far distant from the middle of the band gap (~ 0.3 eV), dominates the conductivity of the material and its compensation is virtually complete (N_d/N_a = 0.99996-0.99998) as predicted by Mandel´s calculations. This result is of primary importance for the Cd_1-xZn_xTe Schottky diode detectors, since the width of the space charge region (active area of detector) in these devices is determined by the concentration of uncompensated impurities rather than the resistivity of the material.