Alloying of CdZnTe (CZT) with selenium has been found to be very promising and effective in reducing the overall concentration of secondary phases (Te precipitates/inclusions) and sub-grain boundary networks in the crystals. These two types of defects are the main causes for incomplete charge collection, and hence they affect the yield of high-quality CZT, resulting in a very high cost for large-volume, high-quality detector-grade CZT detectors. The addition of selenium was also found to very effective in increasing the compositional homogeneity along the growth direction of the CdZnTeSe (CZTS) ingots grown by the traveling heater method (THM) technique. The compositional homogeneity along the growth direction can enhance the overall yield of detector-grade CZTS, which should therefore be possible to produce at a lower cost compared to CZT. The electrical properties and detector performance of the CZTS crystals will be presented and discussed.
Our prior investigations showed that alloying CdTe with selenium results in improved material characteristics, such as a reduction in the concentration of secondary-phase particles, better compositional uniformity and less sub-grain boundary networks, as compared to CdTe/CdZnTe. However, by alloying with Se, the band-gap of CdTeSe is significantly reduced from the value for CdTe, which is the main drawback for high-resistivity CdTeSe compounds useful for radiation detection. In order to increase the band-gap, we are now growing Cd1-xZnxSeyTe1-y crystals for detector applications. The effect of Se alloying with CdZnTe will be discussed in terms of the concentration of secondary phases, stress-related defects such as sub-grain boundaries and their networks. Characterization results for the transport properties of the as-grown materials will also be discussed.