Mechanistic study on In₂O₃atomic layer deposition using InCp and H₂O/O₂

We investigate the atomic-layer-deposition (ALD) mechanism of In₂O₃using the InCp precursor with H₂O and O₂coreactants through density functional theory (DFT) calculations under experimentally relevant conditions. InCp adsorption on hydroxylated SiO₂is strongly favorable, forming In-O bonds and releasing C₅H₆(g) with free-energy gains of -0.48 eV, enabling nearly complete saturation of surface -OH sites. During ALD cycling, the surface-bound In species appear as either Cp-containing or Cp-free motifs, and these two states exhibit distinct oxidation pathways. O₂oxidizes Cp-free In sites to form In-O networks, with a decrease in the free energy by -0.96 eV. However, it cannot remove the remaining Cp ligand. Conversely, H₂O readily converts the Cp ligand into -OH groups, reducing the free energy by -0.56 eV, while it cannot oxidize Cp-free In, which is strongly unfavorable. When supplied together, O₂and H₂O provide complementary reactivity that enables complete oxidation of both surface motifs, consistent with the experimentally observed high growth-per-cycle (GPC) in simultaneous exposure. These mechanistic insights clarify the origins of oxidant-dependent GPC trends and offer guidance for optimizing In₂O₃ALD processes for energy and electronic applications.