Point defects in Cd1−xZnxTe: A correlated photoluminescence and EPR study

Abstract

Cd1−xZnxTe (CZT) is an emerging material for room-temperature x-ray and gamma-ray detectors. The identification and control of point defects and charge compensators in the bulk material are currently important issues. We have used photoluminescence (PL), photoluminescence excitation, and electron paramagnetic resonance (EPR) to characterize point defects in a series of bulk CZT crystals grown by the high-pressure Bridgman technique. Luminescence peaks due to shallow donors, shallow acceptors, and deeper levels, such as VCd-DCd complexes (D = shallow donor), were monitored. This was followed by a detailed study of photo-induced EPR, using a tunable Ti:sapphire laser. There were no EPR signals in the “light off” condition; however, during illumination, an isotropic EPR spectrum due to neutral donors could be observed. The dependence of the donor g value on zinc molar fraction, x, has been determined for the range 0.07<x<0.14. We show that PL and EPR can be combined to give increased quantitative defect analysis in CZT. With resonant tuning of the Ti:sapphire laser, we detected donor concentrations as low as mid-1014cm−3 in detector-grade CZT crystals.