Abstract:

Using the density functional theory (DFT) of quantum chemistry, the adsorption and diffusion of the surface reaction precursor AlCH₃ (MMAl) on the AlN (0001) -Al surface covered with NH₂ and H during MOCVD growth of AlN were calculated and analyzed. By analyzing the surface adsorption energy, diffusion energy barrier, and Mulliken population, etc., the possible stable adsorption structure and diffusion path were determined.The study found that: on the AlN (0001) -Al surface covered with NH₂ and H, with the change of the coverage of NH₂ and H, MMA1 was stably adsorbed at the T4 and H3 positions with similar adsorption probability.As the proportion of NH₂ increases and the proportion of H decreases, MMAl transfers charges to the surface of AlN after adsorption, at the same time its adsorption becomes relatively easy, and diffusion becomes gradually difficult.Compared with before adsorption, the Al-C bond length in MMAl after adsorption is shortened, the bond energy is enhanced, and the detachment of CH₃ is not easy, resulting in a higher probability of introducing C impurities.It shows that MMA1 is not only one of the main reactive substances in growth, but also one of the main sources of introducing C impurities. If there is covering H on the AlN surface, the adsorbed MMA1 will cause the covered H atoms to tend to detach from the AlN surface, which is conducive to subsequent growth.

Key words: AlN, density functional theory, adsorption, diffusion, computational chemistry

摘要：

利用量子化学的密度泛函理论(DFT)，对AlN的MOCVD生长中表面反应前体AlCH₃(简称MMAl)在NH₂和H混合覆盖AlN(0001)-Al面的吸附与扩散进行计算分析。通过分析表面吸附能、扩散能垒及Mulliken数量比例等，确定可能的稳定吸附结构和扩散路径。研究发现：在NH₂与H混合覆盖的AlN(0001)-Al面，随着NH₂与H的覆盖度变化，MMAl均稳定吸附在T4位和H3位，吸附概率相近。随着NH₂比例增多、H比例减少，MMAl吸附后都向AlN表面转移电荷，同时其吸附变得相对容易，扩散变得逐渐困难。与吸附前相比，吸附后MMAl中的Al-C键长缩短，键能增强，不利于CH₃的脱离，导致引入C杂质的概率增高，表明MMAl既可能是生长中主要反应物质之一，同时也是引入C杂质的主要来源之一。若AlN表面存在覆盖H，吸附后的MMAl会促使表面覆盖的H原子倾向于脱离AlN表面，有利于后续生长。

关键词: AlN, 密度泛函理论, 吸附, 扩散, 计算化学