On CdSe Crystal Synthesization And The Improvement Of Single Crystal Growth Technics

CdSe crystal is a new, excellent compound semiconductor material for nuclear radiation detector at room temperature. It has very high resistivity, high atomic number, wide band gap and steady physical and chemical property. At room temperature, it also has good energy resolving power in X-ray and γ-ray detecting. It can be widely used in prospect, scatheless detection, atomic medicine, environment inspection, military and space navigation, etc. At the same time, it is also used as a new material in infrared non-linear optics and solar cells. Now, because of the impurity brought in by synthesization, nonstoichiometry and interphase boundary instability in crystal growth, etc, it is very difficult to grow pure, intact CdSe single crystal. High defect concentration will result in difficult collecting carriers, low energy resolving power and even make the detector invalid. In this experiment, first, we calculate the molar entropy of reaction, molar enthalpy of reaction, Gibbs free energy of reaction and different stiochiometry of CdSe synthesization. Based on the thermodynamics analysis, it discusses the possibility of the direct liquid phase synthesis of CdSe under middle temperature(~650℃). According to the theoretical analysis, rational technical parameters are chosen to conduct a series of synthesis experiments and X-ray diffraction is used to analyze the product of reaction. The result of the experiments shows that we have obtained pure CdSe with stiochiometry when reactive materials use excessive Se (8%～10%) and it proves that the thermodynamics analysis is correct. In addition, compared with the crystal grown before, we find that there is no absorbing peak in 538cm-1 in middle infrared spectrum. It demonstrates that this kind synthesis way can effectively diminish impurities in CdSe raw material, improve the quality of CdSe single crystal. Second, based on the theory of phase equilibrium and steady interphase boundary, we confirm the best temperature and velocity technical parameters. According to the result of study ,we improve the technical parameters of vapor phase growth CdSe and first successfully grow big diameter(Φ20mm), stiochoimetry CdSe single crystal. Its electricity and optics capability test showes that the integrated quality is much better than before. In the end, we analyze the CdSe's life time of positron annihilation and find that with the temperature rising the hole defects in crystal transfer, combine, and at last vanish under the temperature 650℃～800℃. So 650℃～800℃is considered the best anneal temperature for CdSe single crystal. This work is an important part of national "863"program. It will be significant for the further study of CdSe single crystal.