Revisiting the Mechanistic Pathway of Gas-Phase Reactions in InN MOVPE Through DFT Calculations.

Abstract

III-nitrides are crucial materials for solar flow batteries due to their versatile properties. In contrast to the well-studied MOVPE reaction mechanism for AlN and GaN, few works report gas-phase mechanistic studies on the growth of InN. To better understand the reaction thermodynamics, this work revisited the gas-phase reactions involved in metal-organic vapor-phase epitaxy (abbreviated as MOVPE) growth of InN. Utilizing the M06-2X function in conjunction with Pople's triple-ζ split-valence basis set with polarization functions, this work recharacterized all stationary points reported in previous literature and compared the differences between the structures and reaction energies. For the reaction pathways which do not include a transition state, rigorous constrained geometry optimizations were utilized to scan the PES connecting the reactants and products in adduct formation and XMIn (M, D, T) pyrolysis, confirming that there are no TSs in these pathways, which is in agreement with the previous findings. A comprehensive bonding analysis indicates that in TMIn:NH₃, the In-N demonstrates strong coordinate bond characteristics, whereas in DMIn:NH₃ and MMIn:NH₃, the interactions between the Lewis acid and base fragments lean toward electrostatic attraction. Additionally, the NBO computations show that the H radical can facilitate the migration of electrons that are originally distributed between the In-C bonds in XMIn. Based on this finding, novel reaction pathways were also investigated. When the H radical approaches MMInNH₂, MMIn:NH₃ rather than MMInHNH₂ will generate and this is followed by the elimination of CH₄ via two parallel paths. Considering the abundance of H₂ in the environment, this work also examines the reactions between H₂ and XMIn. The Mulliken charge distributions indicated that intermolecular electron transfer mainly occurs between the In atom and N atom whiling forming (DMInNH₂)₂, whereas it predominately occurs between the In atom and the N atom intramolecularly when generating (DMInNH₂)₃.