MOCVD生长AlN/GaN化学反应路径的量子化学研究

Quantum Chemistry Study on Reaction Paths of GaN/AlN Grown by MOCVD

应用量子化学的密度泛函理论,对MOCVD生长GaN/AlN薄膜的反应路径进行理论计算和分析,特别是针对III族TMX（X=Ga,Al）与V族NH3的反应路径与温度的关系进行研究。计算结果表明：当温度T≤473.15 K时,反应自由能△G〈0,TMX与NH3自发生成配位加合物TMX∶NH3;当T≥573.15 K时,△G〉0,TMX∶NH3将重新分解为TMX和NH3。在473.15 K≤T≤573.15 K区间,将存在△G=0,即加合反应达到平衡,反应为双向可逆。随着温度的升高,从加合物变为氨基物DMX∶NH2的反应概率加大。TMX和MMX的直接热解反应均需要高温激活,而DMX变为MMX则较容易发生。当T〉873.15 K时,DMGa变为MMGa的热解反应将自发进行;当T〉1273.15 K时,DMAl变为MMAl的热解反应将自发进行。在自由基CH3参与下,TMX→DMX（X=Ga、Al）的能垒仅为TMX直接热解能垒的一半,约为30~40 kcal/mol;在自由基H参与下,TMGa和TMAl的热解反应能垒更低,约为16~20kcal/mol。因此,自由基H的产生将大大促进TMX的热解。

The reaction paths of GaN / AlN thin film grown by MOCVD were calculated by quantum chemical calculations with density functional theory. In particular,the temperature effect on the reaction paths between the group-III metalorganic source,TMX and group-V source,NH3 was investigated. The results show that： when T≤473. 15 K,TMX and NH3 become ligand adduct TMX∶ NH3 spontaneously;when T≥573. 15 K,TMX ∶ NH3 tends to decompose back into TMX and NH3; when 473. 15 K≤T≤573. 15 K,the adduct reaction is in equilibrium. When temperature increases,the probability of the formation of amide DMX∶ NH2 increases. The pyrolysis of TMX and MMX require high temperatures for activation,while DMX into MMX is easier to occur. When T 873. 15 K,DMGa into MMGa occurs spontaneously; when T 1273. 15 K, DMAl into MMAl occurs spontaneously. With radical CH3 participation,the energy barrier for TMX→DMX（ X = Ga,Al） is in between 30-40 kcal / mol,only halfof that in direct pyrolysis. With radical H participation,the energy barrier for TMX → DMX（ X = Ga,Al） is further reduced,only about 16-20 kcal / mol. Apparently the participation of H radicals will promote the TMX pyrolysis greatly.