Investigations on the reduction of inclusion density in CdZnTe crystals by laser and thermal annealing

CdZnTe crystals are largely employed as substrates for IR devices, X-ray detectors, and electro-optic modulators. One of the main issues affecting device quality is the presence of tellurium inclusions. Different approaches have been suggested for the elimination of tellurium inclusions by means of post growth treatments, such as high temperature thermal annealing of CdZnTe crystals or thermomigration by CO2 laser irradiation. Recently, our group has developed a new system, based on IR microscopy, that allows high resolution imaging and the reconstruction of three-dimensional position of inclusions in CdZnTe crystals. Thanks to this powerful investigation equipment, we report in this work on more complete results relative to both these two approaches. In particular, it is shown that by means of thermal treatments in a controlled atmosphere it is possible to keep high resistivity while getting rid of large tellurium inclusions. Moreover, we have studied tellurium inclusion thermomigration induced by a pulsed Nd:YAG laser irradiation (1.064 micron). The inclusion movement was live-monitored in-situ using the aforementioned IR microscopy system. A much larger thermomigration speed was generally observed with respect to what was reported in the past. Secondly, thanks to the in-situ observations, we concluded that the inclusions migrate at size-dependent speed and tend to separate up to dissolution. Pros and cons,as well as perspectives of these approaches are finally discussed.