Explicit Processing Steps on the Melt Growth of Stoichiometric Cd0.80Zn0.20Te Crystal for High-Energy Radiation Detector

The two critical requirements for the semiconducting cadmium zinc telluride (CdZnTe) crystal to be an efficient room-temperature high-energy radiation detector are (1) high electrical resistivity to reduce the bulk leakage current and (2) minimal structural defects, especially the Te precipitates/inclusions, which act as trapping and recombination centers during charge transport. To fulfill these requirements, it is crucial to (1) reproduce the stoichiometry of the processed crystals toward the intrinsic 1 to 1 ratio of the elements on the two sublattices so as to minimize the carrier concentration caused by the native point defects and (2) minimize various structural defects, especially the Te precipitates/inclusions, by controlling the stoichiometry. Hence, several meticulous practices have been employed during the melt growth process to enhance the yield of bulk Cd0.80Zn0.20Te single crystals of stoichiometric composition with high crystallinity quality. These practices include (A) initializing the homogenization of CdZnTe from pure elements via a traveling zone process, (B) minimizing the contamination of copper (Cu) and other elements by homogenizing the starting material ampoule under external vacuum conditions, (C) reducing the interaction between the sample and the fused silica ampoule during growth through the etching of hydrogen fluoride (HF) with the internal surface of the empty ampoule, (D) promoting the yield of single crystallinity by applying a mechanical pulsed perturbation to the growth ampoule during the nucleation stage of growth, and (E) consistently producing stoichiometric (Cd0.80Zn0.20)1/2Te1/2 crystals via directional solidification under controlled Cd overpressure. In this review, the effects of these practices will be discussed, and the detailed steps of each practice during the directional solidification of (Cd0.80Zn0.20)1/2Te1/2 will be explicitly presented.