AlN-MOCVD生长中气相寄生反应路径

Gas-phase parasitic reaction pathways in AlN-MOCVD growth

利用量子化学的密度泛函理论,研究用于制备紫外光电器件的AlN薄膜在MOCVD生长中的气相寄生反应,计算与气相纳米粒子相关的3种主要多聚物[DMAlNH2]2,[MMAlNH]2,[MMAlNH]3与NH3的反应路径.通过对比不同温度下反应前后的吉布斯自由能差ΔG以及过渡态的活化自由能ΔG*,判断反应发生的方向和概率.结果表明:[DMAlNH2]2存在2条竞争路径,当T<749 K时,反应走[DMAlNH2]2与NH3的双分子反应路径,产物为[Al(NH2)3]2;当T>749 K时,反应趋向于活化自由能更低的、脱去CH4生成[MMAlNH]2的分子内反应路径.[MMAlNH]2,[MMAlNH]3与NH3极易发生双分子反应,脱去CH4,生成更稳定的气相产物[AlNHNH2]2和[AlNHNH2]3.[Al(NH2)3]2,[AlNHNH2]2,[AlNHNH2]3很可能是AlN-MOCVD气相寄生反应的末端粒子,也是AlN生长表面反应和纳米粒子的重要前体.

The density functional theory(DFT)of quantum chemistry was used to study the gas-phase parasitic reactions in AlN-MOCVD growth for UV optoeletronic devices.The reaction pathways of three oligomers of[DMAlNH2]2,[MMAlNH]2 and[MMAlNH]3 with NH3 were investigated,which were related with gaseous nano-particle generation.By comparing the Gibbs free energy difference ofΔG and transition state barrier ofΔG*,the direction and probability of the related reactions were determined.The results show that there are two competition pathways for[DMAlNH2]2.When T is less than 749 K,the reaction path is dominated by bimolecular reaction with[Al(NH2)3]2 as the product.When T is more than 749 K,it is dominated by intramolecular reaction with[MMAlNH]2 as the product,since the reactions always take the path with lower energy barrier.The other two oligomers of[MMAlNH]2 and[MMAlNH]3 both tend to the bimolecular reaction with NH3 to form the more stable gas products of[AlNHNH2]2 and[AlNHNH2]3 with CH4 elimination.The[Al(NH2)3]2,[AlNHNH2]2 and[AlNHNH2]3 are probably the end gas precursors for surface reactions and for nanoparticle generation in AlN-MOCVD process.