Quantum chemical study of trimethylindium and trimethylgallium gas-phase reaction pathways in InGaN MOCVD growth

Density functional theory was used to analyze the formation of InGaN from trimethylindium (TMIn) and trimethylgallium (TMGa) by metalorganic chemical vapor deposition in ammonia in terms of the reaction between trimethyl compounds and NH₃, as well as the subsequent reactions of the key amino species DMInNH₂. The calculation model is established in GAUSSIAN 09, and the results obtained by the calculation model are proved to be reliable by comparing with the previous research results. Reaction pathways were assumed and the Gibbs free energy and activation free energy calculation were conducted at different temperatures. TMIn and TMGa can undergo adduct reactions with the first NH₃ molecule at reaction temperatures below 596 K and 465 K, respectively, but they cannot further react with the second NH₃ molecule to form additional products. The temperature range for adduct reactions between TMIn and NH₃ is wider compared to TMGa and NH₃. In the absence of H radicals in the reaction chamber, DMInNH₂ does not undergo spontaneous CH₃ radical elimination reactions or CH₄ elimination reactions. Instead, DMInNH₂ is more inclined to undergo dimerization reactions and CH₄ elimination reactions with NH₃, leading to the formation of subsequent products, In(NH₂)₃ and dimers. However, in the presence of H radicals in the reaction chamber, H radicals can facilitate the CH₃ radical elimination reaction of DMInNH₂ and also promote the NH₂ radical elimination reaction of In(NH₂)_3, In(NH₂)₂ and InNH₂, enabling these reactions to occur spontaneously within the studied temperature range. Consequently, the subsequent products of DMInNH₂ become indium atoms and dimers.