Abstract:

Using density functional theory(DFT) of quantum chemistry, the gas reaction mechanism in TMG/NH₃/H₂ system is explored, especially the formation of amide DMGNH₂ and its following nano-nucleation path. By calculating the changes of Gibbs free energy along different reaction path under different temperature, the most probable gas products of nucleation of nanoparticles are determined both thermodynamically and kinetically. It is found that DMGNH₂ can be formed by elimination of CH₄ from the adduct or by bimolecular collision when T < 622 K. DMGNH₂ can be directly formed by the bimolecular collision reaction of TMG and NH₃ when T > 622 K. When 662.5 K < T < 939 K, the reactions of dimer [DMGNH₂]₂ to [MMGNH]₂ by successive elimination of CH₄ are easy to occur. When 389 K < T < 734.7 K, the reactions of trimer [DMGNH₃]₃ to [MMGNH]₃ by successive elimination of CH₄ are easy to occur too. However, further elimination of CH₄ from [MMGNH]₂ and [MMGNH]₃ to form [GaN]₂ and [GaN]₃ are both thermodynamically unfavorable, because the changes of Gibbs free energy of the reactions are greater than 0. Thus indicates that [MMGNH]₂ and [MMGNH]₃ are the two probable gas reaction products for the nucleation of oligomers in GaN-MOVPE growth.

Key words: density functional theory, chemical reaction, GaN, MOVPE, nano-nucleation, computational chemistry

摘要：

利用量子化学的密度泛函理论，探讨了TMG(Ga(CH₃)₃)/NH₃/H₂体系中的气体反应机理，特别关注了氨基物DMGNH₂的形成及其后的纳米粒子形核路径。通过计算不同温度下不同反应路径上Gibbs自由能的变化，从热力学和动力学两方面分析纳米粒子形核可能的产物。研究发现当T<622 K时，氨基物DMGNH₂可由加合物TMG:NH₃脱去CH₄生成，也可由TMG和NH₃双分子碰撞直接生成；当T>622 K时，氨基物DMGNH₂直接由TMG和NH₃双分子碰撞反应生成。当 662.5 K<T<939 K时，二聚物[DMGNH₂]₂相继脱去CH₄，变成[MMGNH]₂的反应容易发生。当389 K<T<734.7 K时，三聚物[DMGNH₂]₃相继脱去CH₄，变成[MMGNH]₃的反应容易发生。对于[MMGNH]₂和[MMGNH]₃相继脱去CH₄的反应，因为所有反应的ΔG>0，所以很难生成[GaN]₂和[GaN]₃。因此认为[MMGNH]₂和[MMGNH]₃是GaN-MOVPE低聚物纳米形核最可能的产物。

关键词: 密度泛函理论, 化学反应, GaN, MOVPE, 纳米形核, 计算化学