POINT-DEFECTS IN CD1-XZNXTE - A CORRELATED PHOTOLUMINESCENCE AND EPR STUDY

Cd1-xZnxTe (CZT) is an emerging material for room-temperature x-ray an d 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 excitat ion, and electron paramagnetic resonance (EPR) to characterize point d efects in a series of bulk CZT crystals grown by the high-pressure Bri dgman technique. Luminescence peaks due to shallow donors, shallow acc epters, and deeper levels, such as V-Cd-D-Cd complexes (D = shallow do nor), were monitored. This was followed by a detailed study of photo-i nduced EPR, using a tunable Ti:sapphire laser. There were no EPR signa ls in the ''light off'' condition; however, during illumination, an is otropic EPR spectrum due to neutral donors could be observed. The depe ndence of the donor g value on zinc molar fraction, x,has been determi ned for the range 0.07 < x < 0.14. We show that PL and EPR can be comb ined to give increased quantitative defect analysis in CZT. With reson ant tuning of the Ti:sapphire laser, we detected donor concentrations as low as mid-10(14) cm(-3) in detector-grade CZT crystals.