Low Temperature Thermal Annealing of Detector Grade CdZnTe (CZT) Crystals

ii Electron trapping at second phase Te in CdZnTe (CZT) crystals is presently the limiting factor in the performance of CZT detectors. In this study we have investigated the low temperature (370 – 520K) post growth annealing of detector grade material aimed at dispersing the micrometer scale tellurium. Treatments we performed in vacuum and samples were characterised before and after treatment with special attention being paid to the presence and morphology of second phase in order to establish a correlation between annealing conditions and charge collection parameters. Initial results displayed detrimental consequence to current-voltage quality at top-end annealing temperatures, compromising the mobility-lifetime and detector response of the crystal. Bottom end annealing temperatures rendered very little change in the resistivity of the crystals, but a slight increase in mobility-lifetime (µτprior = 2.98x10-3 cm2V-1 and µτpost = 3.43x10-3 cm2V-1) and increased hole mobility was evident. The project was extended to larger crystals fabricated with a pixellated anode in order to separate bulk and surface resistivity traits. An increased surface resistivity was realised (ρσprior = 1.24 x 109 Ω □ and ρσpost = 2.07 x 1013 Ω□) with little change in bulk resistivity and again an increased mobility-lifetime was witnessed. Upon further inspection, the result is most likely to have arisen due to diffusion of gold at the surface-contact barrier junction, enhancing the ohmic qualities of the contact