Investigation of the formation mechanism and control technology of small-sized structure defects in CdZnTe single crystals grown by the VGF method

Abstract

CdZnTe (CZT) crystals are crucial for room-temperature nuclear radiation detectors, with crystal quality affecting performance. The vertical gradient freezing (VGF) method has been proven effective for producing high-quality CZT single crystals due to the controlled vertical thermal gradients and minimal melt convection. However, large-size CZT crystals prepared by the VGF method commonly exhibit small-sized structure defects, which significantly reduce the effective utilization rate of the material and thereby constrain the widespread application of CZT room-temperature nuclear radiation detectors. Here, we systematically investigated the textural characteristics of small-sized structure defects in CZT single crystals using multi-scale microscopic characterization techniques. It was found that the microstructure of these structure defects primarily consisted of sub-micron twins and polycrystals, and the grain boundary regions exhibited a characteristic enrichment of stacking faults. The formation of small-sized structure defects originated from disturbances in the temperature field during the crystal growth process. Twins and polycrystals induced by locally supercooled regions competed in growth to form a three-dimensional network structure, which eventually evolved into macroscopically visible, distinctive structural defects. Based on these findings, we utilized an integrated experimental and numerical simulation approach to systematically optimize the growth parameters and thermal field distribution during CZT crystal growth. The optimized VGF crystal growth process effectively suppressed the formation of structure defects, and the utilization rate of the fabricated 4-inch CZT single crystals was increased to over 90%. This holds significant importance for the preparation of large-volume, low-cost detectors.