MOVPE生长GaN薄膜的表面吸附和扩散研究

利用量子化学计算方法,对MOVPE生长GaN薄膜的表面反应进行研究.特别针对反应前体GaCH3(简称MMG)在理想、H覆盖和NH2覆盖GaN(0001)面的吸附和扩散进行计算分析.通过建立3×3 超晶胞模型,优化计算了MMG在三种不同覆盖表面的稳定吸附位、吸附能和电子布居,搜寻了MMG在稳定吸附位之间的扩散能垒.计算结果表明:对于三种表面,MMG的稳定吸附位均为T4位和H3位,H3位比T4位略微稳定.MMG在NH2覆盖表面吸附能最大,在H覆盖表面吸附能最小,在理想表面吸附能居中.MMG中的Ga与不同的表面原子形成的化学键的键强的大小顺序为:Ga-N>Ga-Ga>Ga-H.相比于理想表面和H覆盖表面,MMG在NH2覆盖表面的扩散能垒最大,因此表面过量的NH2会抑制MMG的扩散.

Surface Adsorption and Diffusion of GaN Thin Film Grown by MOVPE

Based on the quantum chemistry method, the surface reactions of GaN MOVPE growth were investigated.In particular, the adsorption and diffusion processes of GaCH3 (MMG) on ideal, H-covered and NH2-covered GaN(0001)-plane were calculated and analyzed.By establishing a 3×3 supercell model, the stable adsorption sites, adsorption energies and electron population of MMG on three different surfaces were searched and calculated, and the diffusion energy barriers were also determined.The calculated results show that the stable adsorption sites of MMG are T4 and H3 for all three surfaces, and H3 is slightly more stable than T4.The adsorption energy of MMG on the NH2-covered surface is the largest, that on the H-covered surface is the smallest, and that on the ideal surface is in between.The order of bond strengths between Ga in MMG and the surface adsorbent atoms is Ga-N>Ga-Ga>Ga-H.MMG is less likely to diffuse on the NH2-covered surface than on the ideal and the H-covered surfaces, Therefore, excessive NH2 on the surface inhibits the surface diffusion of MMG.