MOCVD生长InN气相反应路径的量子化学研究

Quantum chemistry study on gas reaction path in InN MOCVD growth

利用量子化学的密度泛函理论,对MOCVD生长InN的气相反应路径进行较全面的计算分析,通过计算不同温度下各反应的Gibbs能差和反应能垒,分别从热力学和动力学角度确定从TMIn/NH_(3)生长InN的主要气相反应路径。研究发现:当载气为N_(2)时,InN生长的气相反应路径主要为热解路径与加合路径的竞争。在高温(T>873.0 K)时以TMIn的热解为主,在低温(T<602.4 K)时以TMIn与NH_(3)的加合反应为主,在中温(602.4 K<T<873.0 K)时以加合物TMIn:NH_(3)的分解反应为主。当载气为H_(2)时,由于气相热解和表面反应将产生H和NH_(2)自由基,H自由基将加速TMIn的热解,NH_(2)自由基将与TMIn、DMIn等反应生成氨基物DMInNH_(2)。H自由基还会与氨基物反应,在高温衬底附近生成InNH_(2),从而使表面反应前体由传统的MMIn和In变为InNH_(2)。研究结果给出了InN MOCVD气相反应路径与温度的定量关系,以及H和NH_(2)自由基的参与引起的新的气相反应路径。

By performing density functional theory(DFT)calculations of quantum chemistry,the gas-phase reaction paths in the InN MOCVD process are systematically investigated.By calculating the changes of Gibbs energy(ΔG)and the energy barrier(ΔG^(*)/RT)of all proposed steps at different temperatures,the main gas reaction paths in InN growth from TMIn/NH3 are determined.According to computational results,when N_(2) is used as the carrier gas,the TMIn pyrolysis path competes with the adduct path could for the main reaction.The TMIn pyrolysis dominates the gas reaction path at high temperatures(T>873.0 K),whereas at low temperature(T<602.4 K),the adduct reaction to form TMIn:NH_(3) is favored,and the decomposition of TMIn:NH_(3) is predominant at medium temperature(602.4 K<T<873.0 K).When H_(2) is used as the carrier gas,the H and NH_(2) radicals can be generated through gas pyrolysis as well as surface reactions.Because H radicals can accelerate the TMIn pyrolysis and NH_(2) radicals canreact with TMIn and DMIn to generate DMInNH_(2),both radicals can disrupt InN MOCVD process.The formed amides can further react with H radicals and generate InNH_(2) near the high temperature substrate,and hence swaps the surface reaction precursors from MMIn and In to InNH_(2).Additionally,this study also illustrate how changing reaction temperature could affect InN MOCVD gas-phase pathways,and reveals novel reaction pathways with the interferences from H and NH_(2) radicals.