Abstract
Because of its ideal band gap, high density and high electron mobility-lifetime product, cadmium zinc telluride (CdZnTe or CZT) is currently the best room-temperature compound-semiconductor X- and gamma-ray detector material. However, because of its innate poor thermo-physical properties and above unity segregation coefficient for Zn, the wide spread deployment of this material in large-volume CZT detectors is still limited by the high production cost. The underlying reason for the low yield of high-quality material is that CZT suffers from three major detrimental defects: compositional inhomogeneity, high concentrations of dislocation walls/sub-grain boundary networks and high concentrations of Te inclusions/precipitates. To mitigate all these disadvantages, we report for the first time the effects of the addition of selenium to the CZT matrix. The addition of Se was found to be very effective in arresting the formation of sub-grain boundaries and its networks, significantly reducing Zn segregation, improving compositional homogeneity and resulting in much lower concentrations of Te inclusions/precipitates. Growth of the new quaternary crystal Cd1−xZnxTe1−ySey (CZTS) by the Traveling Heater Method (THM) is reported in this paper. We have demonstrated the production of much higher yield according to its compositional homogeneity, with substantially lower sub-grain boundaries and their network, and a lower concentration of Te inclusions/precipitates.
Highlights
X-ray and gamma-ray detectors have broad applications, ranging from medical imaging, non-proliferation and national security to astrophysics
Though the Te inclusions can be eliminated by annealing under cadmium vapor, the process produces star-like defects that are not visible in infra-red (IR) transmission microscopy
These star-like defects are 50–100 times larger than the Te inclusions and act as trapping centers, which can severely affect the charge-transport properties[23]. To mitigate these problems presently suffered by CZT material, we adopted the growth of a new quaternary material Cd1−xZnxTe1−ySey (CZTS)
Summary
We have grown two-inch diameter Cd0.9Zn0.1Te0.93Se0.07 ingots by the Traveling Heater method (THM). It is to be noted that, even though the ingot was cooled rapidly to room temperature after the termination of growth, no thermal stresses and sub-grain boundary networks are evident in the X-ray topographic image. This type of image indicates that the selenium plays a major role in effective solution hardening of the CZTS matrix resulting in growth of CZTS free from sub-grain boundary networks. The present experimental results clearly demonstrate the role of Se as a promising additive in CZT matrix for effectively enhancing the compositional homogeneity of the as-grown ingot and reducing the concentration of size and distribution of Te inclusions/precipitations. A lower concentration of secondary phases and the absence of sub-grain boundary network in CZTS indicate tremendous potential of CZTS for better detector quality and a much lower production cost
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