Carbon Coating and Defects in CdZnTe and CdMnTe Nuclear Detectors

CADMIUM zinc telluride (CdZnTe) and cadmium manganese telluride (CdMnTe) are prime materials for detecting X-rays and gamma-rays at room temperature due to their high average atomic numbers that are essential to having high stopping -power for incident high-energy electromagnetic radiations. A major obstacle in developing CdZnTe and CdMnTe detectors lies in growing crystals free from defects, such as Te inclusions, dislocations, sub-grain boundary networks, and precipitates. We present the results of our study of the relationship between carbon coating of the growth ampoule and dislocations in CdZnTe and sub-grain boundary networks in CdMnTe, grown by Bridgman method. For the CdZnTe crystals, a carbon-coating of 2 Am on the ampoule generated fewer dislocations than did a thinner 0.2 - mu m carbon-coated one. Furthermore, the ampoule's design (normal- or tapered-shape) did not affect the densities of etch pits as much as did the thickness of the carbon-coating. For a CdMnTe ingot with a carbon coating of about 2 mu m, created by cracking spectroscopic-grade acetone at rsd 900 degrees C, we observed very few grain boundaries and grain-boundary networks.