Growth Of CdZnTe Single Crystals And Fabrication Of CdznTe Room Temperature Nuclear Radiation Detectors

CdZnTe(CZT) is a new developing compound semiconductor, and has been regarded as leading materials for room temperature nuclear radiation detectors. Due to its disadvantageous physic properties, it is very difficult to grow CZT single crystals with high resistivity and perfect crystalline. Until now, there is no suitable method to grow high resistivity CZT single crystals, and the application of CZT is limited.In this paper, the forming mechanism of Cd vacancies, which affect the resistivity of CZT crystal, has been studied. To control the concentration of Cd vacancies, a new method by which the Cd vacancies were compensated with excess Cd in the Cd rich starting materials has been developed. Through improved method, large single crystals with high resistivity and perfect crystalline were gotten, and CZT room temperature nuclear radiation detectors were fabricatedDuring the process of crystal growth, the vapor pressure upon the melt got very much. By freezing the vapor quickly into solid, the partial pressures of Cd, Zn and Te were measured. The result shows that nearly 90% of the vapor is Cd vapor. So it can be seen that mere is a loss of Cd in the melt, and Cd vacancies formed in the CZT single crystals. There are several methods to control the concentration of Cd vacancies, such as High Pressure Bridgeman Method, Growing crystal under a vapor provided by a Cd source, Growing crystal from Cd rich starting materials and annealing CZT in Cd vapor. The last two methods were studied in this paper. Growing crystals from Cd rich starting material has not been reported, but the investigation shows that it is a simple and promising method of growing high resistivity CZT single crystals.To ensure the high quality of CZT single crystals, the CZT compounds weresynthesized by temperature oscillation; the growth ampoule was descended with rotating. The optimal growth parameters were obtained by systematic growth experiments; while the thermal gradient at the crystal-melt interface was 10C/cm, the growth rate is 0.5mm/h and the lost Cd was compensated by excess Cd in the Cd rich starting materials. CZT single crystal 20mm in diameter and 50mm in length can be gotten. The resistivity, Infrared transmission, EPD and concentration of electron traps of as-grown crystals are 2 X 1010Q-cm, 50%, 5 X 104/cm2 and 4 X 1010/cm3 respectively. The research result of annealing CZT wafers in Zinc vapor shows that the concentration of Cd vacancies was decreased, and the resistivity increased nearly five magnitudes.The fabrication of CZT room temperature nuclear radiation detectors has been studied and it was found that the Carbon /Cdo.gZnoiTe contact is Ohmic, the detector with Carbon contact is sensitive to 241Am source, the energy resolution for ^Am 59.5KeV line was about 28% and there is no polarization.All results of this study show that by descending ampoule with rotating, detector grade CZT single crystals can be grown from Cd starting materials synthesized with temperature oscillation.