Compensation processes in high-resistivity CdZnTe crystals doped with In/Al

Abstract

The high resistivity performances for aluminum/indium doped Cd0.9Zn0.1Te crystals (CZT:Al/CZT:In), grown via the modified vertical Bridgman method and under excess Cd/Te conditions, were investigated by the relationship between Al/In dopant behaviors and defects induced by crystal growth. Subsequently, their defects compensation processes responsible for high resistivity were proposed by thermally stimulated current spectroscopy. It was revealed that the donor levels from impurity Al/In are too shallow to account for the Fermi level pinned near the mid-gap of CZT materials. Considering the growth of CZT:Al crystal under Cd-rich condition, the doubly ionized Cd interstitial (Cdi2+) as a deep donor was formed with an activation energy of 0.554eV. Correspondingly, a deep donor level of doubly ionized Te antisite (TeCd2+) located at 0.704eV was observed in CZT:In crystal grown under Te-rich condition. In addition, the Fermi level dominated by deep level defects were evaluated at 0.716eV for CZT:Al and 0.740eV for CZT:In by the temperature-dependent resistivity using current-voltage measurements, which almost approach the mid-gap. We therefore suggest that these deep donor defects (TeCd2+/Cdi2+) can stabilize the Fermi level deep near the mid-gap and thus result in high resistivity.