GaN-MOVPE寄生反应的密度泛函理论研究

Density functional theory study on parasitic reactions of GaN-MOVPE

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。

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.