Adsorption mechanism of dimeric Ga precursors in metalorganic chemical vapor deposition of gallium nitride

Gallium nitride (GaN) has attracted significant interest as a next-generation semiconductor material with various potential applications. During metalorganic chemical vapor deposition (MOCVD) of GaN using trimethyl gallium (TMG) and NH₃, dimeric precursors are produced by gas-phase reactions such as adduct formation or thermal decomposition. In this work, the surface adsorption reactions of monomeric and dimeric Ga molecules including TMG, [(CH₃)₂Ga(NH₂)]₂, and [(CH₃)GaNH]₂ on the GaN surface are investigated using density functional theory calculations. It is found that [(CH₃)₂Ga(NH₂)]₂ is the most predominant form among the various dimeric precursors under typical GaN MOCVD process conditions. Our results indicate that the dimeric [(CH₃)GaNH]₂ precursor, which is generated through the thermal decomposition of [(CH₃)₂Ga(NH₂)]₂, would have higher reactivity on the GaN surface. Our work provides critical insights that can inform the optimization of GaN MOCVD processes, leading to advancements in GaN-based high-performance semiconductors.