Study on thermal annealing of cadmium zinc telluride (CZT) crystals

Abstract

Cadmium Zinc Telluride (CZT) has attracted increasing interest with its promising potential as a room-temperature nuclear-radiation-detector material. However, different defects in CZT crystals, especially Te inclusions and dislocations, can degrade the performance of CZT detectors. Post-growth annealing is a good approach potentially to eliminate the deleterious influence of these defects. At Brookhaven National Laboratory (BNL), we built up different facilities for investigating post-growth annealing of CZT. Here, we report our latest experimental results. Cd-vapor annealing reduces the density of Te inclusions, while large temperature gradient promotes the migration of small-size Te inclusions. Simultaneously, the annealing lowers the density of dislocations. However, only-Cd-vapor annealing decreases the resistivity, possibly reflecting the introduction of extra Cd in the lattice. Subsequent Te-vapor annealing is needed to ensure the recovery of the resistivity after removing the Te inclusions.

What causes high resistivity in CdTe

“…Many attempts have been made to remove Te-inclusions and precipitates by annealing CdTe and CZT under Cd overpressure. This usually results in decrease in resistivity [63][64][65][66], consistent with our results. Figure 8 shows that Cd 2+ i and V 2+ Te have similar formation energies.…”

Investigation of crystallographic and detection properties of CdTe at the ANKA synchrotron light source

“…By comparing the topography map of the CdTe sensor with its X-ray flood image in figure 1a, it is possible to correlate the topography features with the charge collection variation of the detector. As described in [5][6][7][8][9], subgrain boundaries are defects where charge carriers tend to accumulate. Due to that, in the crystal regions around the boundaries potential barriers are formed which affect the local electric field.…”

“…However, there are still some material issues to be investigated such as the presence of Te inclusions, sub-grain boundaries and small inhomogeneities that may degrade the device performance [5]. Te inclusions, which form during the CdTe growth, trap the charge carriers reducing the charge collection efficiency [6,7]. Grain boundaries can be considered as walls of edge dislocations, whose dangling bonds accumulate space charge and attract impurities [8,9].…”