New insights for uniform and large-volume CdZnTe and CdMnTe detectors

CdZnTe (CZT) and CdMnTe (CMT) materials come into the spotlight for room-temperature semiconductor detectors. Nonethelss, both materials still have limitations for the production of economical, uniform, and large-volume devices due to the zinc (Zn) segregation in CZT and manganese purity in CMT. The effective segregation coefficient of Zn in the CdTe host is nearly 1.3, so about 5-6% of Zn deviation has been reported in Bridgman-grown CZT (Zn=10%) ingots. Such Zn non-uniformity limits the cutting of the ingot parallel to the crystal growth direction for producing large-volume CZT detectors due to the signal non-uniformity that would be generated by the band-gap variations. However, our recent findings show that the Zn segregation can be controlled by the specific thermal environment. The high residual impurities in the starting source materials, especially for manganese, were obstacles for obtaining high-performance CMT detectors. The purification of manganese telluride (MnTe) by a floating Te melt-zone proved to be very effective, and CMT detectors fabricated with purified material give a 2.1% energy resolution for 662 keV associated with a ¹³⁷Cs gamma source.