Cs/GaN(0001)吸附体系电子结构和光学性质研究

Electronic structure and optical properties of Cs/GaN(0001) adsorption system

采用基于第一性原理的密度泛函理论平面波超软赝势方法计算了1/4ML Cs原子吸附(2×2)GaN(0001)表面的吸附能、能带结构、电子态密度、电荷布居数、功函数和光学性质.计算发现,1/4ML Cs原子在GaN(0001)表面最稳定吸附位为N桥位,吸附后表面仍呈现为金属导电特性,Cs原子吸附GaN(0001)表面后主要与表面Ga原子发生作用,Cs6s态电子向最表面Ga原子转移,引起表面功函数下降.研究光学性质发现,Cs原子吸附GaN(0001)表面后,介电函数虚部、吸收谱、反射谱向低能方向移动.

We employ first-principles to calculate the adsorption energy, the band structure, the density of states, the charge populations, the work function and the optical properties of 1/4ML Cs adsorption on （2 × 2） GaN（0001） surface using the density-functional theory within a plane-wave ultrasoft pseudopotential scheme. The results show that the most stable position of Cs adatom on GaN（0001） surface is at the bridge site of N atoms for 1/4 coverage. The surface of GaN（0001） shows still metallic character after adsorption. Cs adatom affects mainly Ga atoms at surface. The transfer of Cs6s state electrons to Ga atoms at outmost layer leads to the decrease of work function. By analysis of optical properties, we can see imaginary part of dielectric function, absorption spectrum and reflected spectrum shift toward low energy after Cs adsorption.