ZnSe电子结构与性质的第一性原理研究

【作者】 季正华；

【导师】 曾祥华；

【作者基本信息】 扬州大学 ， 凝聚态物理， 2009， 硕士

【摘要】 Ⅱ-Ⅵ族半导体发光材料具有优异的光电催化及光电转化活性等特性,已广泛应用于光学材料、太阳能材料、压电晶体和激光材料等领域.而ZnSe被认为是一种较好的制备蓝绿激光器的材料,已引起世界各国科研人员的广泛关注.目前,对ZnSe的电子结构、半导化掺杂、高压化途径、导电模型、缺陷态、表面/界面态等方面已有相关的理论和实验结果,但是在高压化途径、杂质和缺陷对材料半导化、光学性能以及相关性质的影响机理仍存在着分歧.本文采用基于密度泛函理论框架下的平面波赝势方法,对ZnSe材料的高压化途径、本征Zn缺陷、替代性V掺杂、电子结构、光学性质等进行研究,为制备高质量的ZnSe半导体材料及其应用提供理论依据.主要研究内容及结果如下:一、系统地计算了闪锌矿结构ZnSe晶体不同压强下平衡时的晶格常数、总能量、电子态密度分布、能带结构、光反射与吸收系数;详细讨论了高压下ZnSe的电子结构,并且结合实验结果定性地分析了高压下的光学性质.计算结果表明:随着压强的增大,晶格常数和键长在不断变小,总能量不断升高,Zn原子和Se原子的态密度峰都有不同程度的变化,有向低能量移动的趋势,闪锌矿结构ZnSe晶体在压强为26.5 Gpa时由直接带隙半导体变成了间接带隙半导体.二、对闪锌矿结构(ZB)和岩盐结构(RS)的ZnSe在0~20 Gpa高压下的几何结构、态密度、能带结构进行了计算研究,分析了闪锌矿结构ZnSe和岩盐结构ZnSe的几何结构,在此基础上,研究了ZnSe的结构相变、弹性常数、成键情况以及相变压强下电子结构的变化机制,结果发现:通过焓相等原理得到的ZB相到RS相的相变压强为15.3 Gpa,而由弹性常数判据得到的相变压强为11.52 Gpa,但在9.5 Gpa左右并没有发现简单立方(SC)相的出现;在结构相变过程中,sp3轨道杂化现象并未消除,Zn原子的4s电子在RS相ZnSe的导电性中起主要贡献.三、对V掺杂和Zn空位ZnSe闪锌矿结构进行了优化,讨论了电子结构以及Zn空位下的光学性质,对ZnSe半导体的自补偿效应和光催化性能做了探讨.结果表明:V掺杂与Zn空位ZnSe体系,并没有因为杂质或空位的存在而发生晶格畸变,V掺杂ZnSe体系由于杂质原子能级的存在,费米面附近的能级连续,从而表现出明显的金属性,Zn空位ZnSe体系由于Zn空位能级的存在,导致费米面能量降低,价带顶能级处于半满状态,电导率和发光性能大大提高,使得介电峰拓展到红外区,为ZnSe运用在红外光催化实验中提供了理论依据.更多还原

【Abstract】 Because of their excellent photoelectric conversion and photo-electro-catalytic activity,Ⅱ-Ⅵsemiconductor light-emitting materials have been used as optical materials, solar energy materials, piezoelectric crystals, laser materials and other fields. And ZnSe is considered to be a better candidate for the preparation of blue-green laser material, which has been attracted many researchers’attention. At present, some theoretical and experimental investigations have been done on electronic structure,doping,conductivity model, defect states,surfaces and interface of ZnSe, but there are still some discrepancies, such as the route of the phase change under high pressure, the effects of impurity and defect on optical properties of ZnSe. Therefore using the first principles method, the electronic structures and optical properties for the different phases of ZnSe,the intrinsic Zn vacancies and doped with vanadium have been investigated with ultra-soft pseudo-potential approach of the plane wave based upon the Density Functional Theory (DFT). The main contents are as the following:1. The electronic structure and optical properties of zinc blended structure ZnSe under different pressures have been calculated. And the total energy, density of state, energy band structure, and optical absorption and refection properties have been discussed. Furthermore, the changes of electron structure, band structure and optical properties under high pressure have been analyzed in comparison with the experimental and theoretical data.2. Geometric structures, density of states and band structures of zinc blended structure and rock salt structure of ZnSe at different pressures (from 0 Gpa to 20 Gpa) have been calculated. Based on those results, the structure of the ZnSe phase transitions, elastic constants, bonding and phase transition under pressure have been discussed. From the principle of enthalpy for the ZB and RS ZnSe, the pressure at the phase transition is equal to 15.3 Gpa, which is greater than the results of 11.52 Gpa from the elastic constants of the phase transition criterion. And the change of phase to SC has not been found at the pressure of 9.5 Gpa; and the sp3 hybrid orbital have not been eliminated during the structure phase transition, while the 4s electronic state of Zn atom has a major contribution to the conductivity in RS phase.3. The geometric structure of V-doped and Zn vacancy for blended structure ZnSe have been optimized firstly, then the electronic structures and optical properties of the Zn vacancy in ZnSe with self-compensation effect and photo catalytic properties have been discussed. The results gives that, for V-doped ZnSe and Zn vacancy, there was no lattice distortion because of the existence of impurities; for V-doped ZnSe system, due to the existence of the impurity atomic energy level, the energies near Fermi level become continuous, and it shows the metal properties, while for the Zn vacancy the Fermi energy declines, and the conductivity and luminescence greatly increase. The dielectric peak is extended to the infrared area, so ZnSe containing Zn vacancy can be applied to the infrared optical catalytic experiments.更多还原