Segregation Study of Some Impurities in Three Purification Process of CdTe Ingots

Several attempts were made during the last 3 decades to improve the quality of CdTe in order to enhance its efficiency as material for nuclear and photovoltaic devices. These attempts considered the high values of impurity segregation coefficients and the contamination problems due to handling at high temperature. In this study, we prepared three high purity CdTe single crystals with high resistivity. The three starting Te samples were purified through three purification processes: horizontal zone refining, vacuum distillation, and by combining both processes. Purities were characterized, by determining the concentration of 22 impurities by Atomic Absorption (AASGF), for the three kinds of tellurium ingots and the corresponding elaborated CdTe materials. A series of four effective segregation coefficients for metallic impurities: Ag, Al, Cu, and Fe were found in CdTe. Their high values confirmed the difficulty to remove them by the purification processes using the segregation phenomenon. In addition, the low concentration values of impurities in CdTe samples (≥ 6N purity) make from our CdTe high quality electronic grade materials.