Post-growth annealing of Bridgman-grown CdZnTe and CdMnTe crystals for room-temperature nuclear radiation detectors

Abstract

Bridgman-grown cadmium zinc telluride (CdZnTe or CZT) and cadmium manganese telluride (CdMnTe or CMT) crystals often have Te inclusions that limit their performances as X-ray- and gamma-ray-detectors. We present here the results of post-growth thermal annealing aimed at reducing and eliminating Te inclusions in them. In a 2D analysis, we observed that the sizes of the Te inclusions declined to 92% during a 60-h annealing of CZT at 510°C under Cd vapor. Further, tellurium inclusions were eliminated completely in CMT samples annealed at 570°C in Cd vapor for 26h, whilst their electrical resistivity fell by an order of 102. During the temperature-gradient annealing of CMT at 730°C and an 18°C/cm temperature gradient for 18h in a vacuum of 10−5 mbar, we observed the diffusion of Te from the sample, so causing a reduction in size of the Te inclusions. For CZT samples annealed at 700°C in a 10°C/cm temperature gradient, we observed the migration of Te inclusions from a low-temperature region to a high one at 0.022μm/s. During the temperature-gradient annealing of CZT in a vacuum of 10−5mbar at 570°C and 30°C/cm for 18h, some Te inclusions moved toward the high-temperature side of the wafer, while other inclusions of the same size, i.e., 10µm in diameter, remained in the same position. These results show that the migration, diffusion, and reaction of Te with Cd in the matrix of CZT- and CMT-wafers are complex phenomena that depend on the conditions in local regions, such as composition and structure, as well as on the annealing conditions.