Electron paramagnetic resonance investigation of donor impurities in CdZnTe grown by different techniques

Cadmium zinc telluride (CdZnTe) is being developed for room- temperature x-ray and gamma ray detectors. Identification and control of point defects and charge compensators are currently important issues. We have used electron paramagnetic resonance (EPR) and photo-induced EPR to evalute shallow-donor defects in CdZnTe crystal grown by two different techniques. Samples grown by the high-pressure Bridgman technique and a crystal grown by horizontal Bridgman at IMARAD and doped with indium were included in this study. Prior to the EPR investigations, we performed liquid-helium photoluminescence (PL) in order to examine the radiation recombination paths and identify the presence of other defects in these crystals. Spectra were obtained showing sharp excitonic lines, shallow and deep DAP emission bands, and a deeper 1.1 eV emission. The PL data help define the optical excitation range used in photo-EPR measurements. The photo-EPR data obtained from our samples is used to determine the concentration of isolated donor centers, while the EPR signal present under no illumination gives a measure of the net compensation. We also report the excitation wavelength dependence of the isotropic EPR signal from the shallow donors.