闪锌矿GaN(110)表面原子和电子结构的理论计算

Theoretic Calculation of Atom and Electronic Structure for Zinc-blende GaN (110) Surface

在密度泛函理论的基础上,采用平面波赝势方法计算了立方GaN(110)表面的原子和电子结构。结构优化表明最表层原子都向体内弛豫,且金属Ga原子弛豫幅度比非金属N原子大,同时各层层间距呈交错分布。表面弛豫后,最表层原子发生键长收缩的弛豫特性,表面Ga原子趋于形成sp2杂化得到的平面型构形,而表面N原子趋于形成p3型锥形结构。另外,理想立方GaN(110)表面在带隙中有两个明显的表面态,经过弛豫后,分别向价带和导带方向移动,并解释了导带底附近的表面态移动的幅度比价带顶附近的表面态大的原因主要由于表面Ga、N原子弛豫幅度不同引起的。此外,弛豫后,表面电荷重新分布,Ga原子周围的部分电子转移到N原子上。

Electronic structures of the （110） surface of cubic phase GaN have been calculated by using plane-wave pseudopotential method based on density functional theory. Geometry opti- mization indicates that the atoms on the first layer move inwards, the relaxation displacement of Ga is larger than that of N. After surface relaxation, the relaxation characteristic of the first layer shows shorting in the length of Ga-N bonds. The Ga atoms tend to a planar shape like sp2 bonding; however, N atoms tend to a taper shape like p3 bonding. Meanwhile, the ideal cubic GaN （110） surfaces have two obvious surface states in the band gap. After relaxation, these two surface energy levels move towards the valence band and the conduction band respectively. The moved amplitude of the surface state near the conduction band is larger than that of the surface state near the valence band. This difference is attributed to the difference of the relaxation dis- placement of the surface atoms. Furthermore, after the relaxation, the surface charges have changed, some electrons around Ga atoms are transferred to N atoms.