Study On Crystal Growth Of High Resistivity Cd_0.9Zn_0.1Te Under Partial Pressures Control And Their Subsequent Annealing

Cd_1-xZn_xTe radiation detector not only can work at room temperature, but also has high detection efficiency and good energy resolution for Y - and x- ray. So it has been used in many fields such as nuclear security, environment inspecting, medicine diagnoses and sphere physics research. The high-quality Cd_1-xZn_xTe crystal material is the key issue for developing high-performance Cd_1-xZn_xTe nuclear-detectors. Presently commercial Cd_1-xZn_x crystals are mostly prepared by HPVB method in the world and the resistivity of the as-grown crystal reached up to 10¹¹ Ωcm. However, the method needed complex equipments and the useable part of the as-grown crystal was lower than 4%, the cost of crystal was very high. At present, the research on crystal growth of Cd_1-xZn_xTe in the world is focus on how to grow crystal with high resisitivity, high quality and low cost by the LPVB method, but there are still some problems on basic theory and technology unresolved, so it is of important academic significance and applied worth to perform the research on these problems. In this paper, we systematically studied the preparation theory and technology of Cd_0.9Zn_0.1Te crystal. The main contents and conclusions of the paper are summarized as follows:Finite element method (FEM) was used to simulate the growth process of Cd_0.9Zn_0.1Te crystal and the effects of different crucible moving rates on crystal growth rate and solid-liquid interface configuration were studied as well. Thermal conduction, convection, radiation and phase-change process were considered in our calculation model. The intrinsic relationship between the interface shape and the crucible descending rate was discussed in details. In addition,Cd_0.9Zn_0.1Te crystal growth experiments were carried out, experimental results and the simulation results were compared as well. Simulation results show that when crucible descends at the rate of about lmm/h, nearly flat solid/liquid interface can be attained which is very helpful to gain Cd_0.9Zn_0.1Te crystal with uniform composition distribution in the radial direction and higher quality. And the simulation result is well consistent with that of experiments.Equilibrium partial pressures over Cd_1-xZn_xTe and Cd_1-xZn_x melt with different composition in different temperatures were estimated by thermodynamic relationship based on previous work, and the Cd, Zn partial pressures of P_Cd=4.037×10⁵ Pa andpZn=4.995xl04 Pa over Cdo.9Zno.1Te melt at the melting temperature of 1393K were firstly obtained, which are consistent with those over the Cdj_xZnx melt at the temperature of 1195K.A new synthesis method called EPS (Evaporating Pressure Synthesis) was performed to synthesize ZnTe, which overcame the weaknesses of conventional synthesis method with high synthesis temperature, insufficient synthesis, severe reaction and easy to explode, and homogeneous ZnTe was obtained.MVB method was used to grow the Cdo.9Zno.1Te crystals under Cd/Zn partial pressures provided by Cdo.siZno 19 alloy reservoir in our lab, we succeed to obtain the high quality CdogZno.iTe crystals. The best result for the resistivity, which has reached up to about l.l><10l0Q-cm, has been obtained under the equilibrium partial pressures. FWHM of the X-ray rocking curve was about 53'", which indicates excellent structural integrity of the crystal. The etch pit density of the crystal was 7X 104cm"2 on average. Infrared transmissivity of the crystal was up to 60% in the range of 5000⁴50cm'\ and the radial variation of Zn concentration was less than 0.2al%. In addition, the relationship between the resistivities of Cdo.9Zno.1Te crystals and the partial pressures controlled during the crystal growth was also obtained.The upper limit value of annealing temperature was determined by exploring the high-temperature phase of CdTe. Based on the estimation of equilibrium partial pressures over Cdi_xZnx melt, the as-grown high resistivity Cdo.9Zno.1Te slices have been annealed under controlled Cd/Zn equilibrium pressures provided by Cdi_xZnx alloy source. The relationship between the properties of Cdo.9Zno.1Te slices and the annealing parameters such as annealing temperature, holding time. Cd/Zn partial pressure have been discussed. The results show that the integrality of Cdo.9Zno.1Te slices with high resistivity were improved after annealing, Infrared transmissivity of the slices can be raised by 3% up to 65% in the range of 5000⁴50cm'' and their resistivities were further raised. In addition, the Cdo.9Zno.1Te with relative low resistivity of 7.0 X 104Q-cm slices can be raised by 4 orders, up to 6.97 X 108fi-cm, the value of IR of the slices an be raised by over 10%. up to 64% in the range of 5000⁴50crrf', and after they were annealed under optimizing conditions.A novel process of diffusion into as-grown Cdo.9Zno.1Te slices by In as gas-doping...