应力条件下GaN电子结构及光学性质研究

Study on Electronic Structure and Optical Properties of GaN under Pressure

采用密度泛函理论框架下的第一性原理平面波计算方法,系统研究了不同应力作用下GaN的电子结构和光学性质,对比分析了外压调制对GaN的能带结构、态密度和光学性质变化的影响。计算结果表明:随着外应力的逐渐增加,Ga—N的键长逐渐变小,布局数逐渐增加,共价性明显增强,离子性减弱。电子结构计算结果显示导带向高能方向漂移,而整个价带向低能方向漂移,禁带带宽明显被展宽,Ga原子的3d态电子与N原子的2p态电子的杂化程度增强。光学性质计算结果揭示了在没有应力的作用下,在1.6 eV附近开始出现吸收边。随着外应力的逐渐增大,GaN的复介电函数和吸收谱向高能方向漂移,光谱发生了明显的蓝移现象,进而提高了光电转换效率。

Electronic structure and optical properties are systematically investigated by using first-principles plane-wave calculation method based on density functional theory, and the changes in the band structure, density of states and optical properties are comparatively analysed for GaN under pressure. The calculated results indicate that Ga--N bond lengths become shorter, the populations become larger, the covalent becomes stronger and the ionic becomes weaker when the pressure increases. The calculated electronic structure shows that the conduction bands move to high energy direction, while the whole valence bands shift to low energy direction, the band gap becomes wider, the hybridization of 3d states electron of Ga atoms and 2p states electron of N atoms is enhanced significantly. Results of optical properties reveal that absorption spectrum occurs absorption edge near 1.6 eV when there is no stress. With the pressure increasing, the complex dielectric function and absorption spectra of GaN move towards high energy, the absorption spectrum occurs obvious blue shift and the photoelectric conversion efficiency is improved.