Mechanistic study on In ₂ O ₃ atomic layer deposition using InCp and H ₂ O/O ₂

Abstract We investigate the atomic-layer-deposition (ALD) mechanism of In ₂ O ₃ using the InCp precursor with H ₂ O and O ₂ coreactants through density functional theory (DFT) calculations under experimentally relevant conditions. InCp adsorption on hydroxylated SiO ₂ is strongly favorable, forming In–O bonds and releasing C ₅ H ₆ (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. O ₂ oxidizes 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, H ₂ O 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, O ₂ and H ₂ O 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 In ₂ O ₃ ALD processes for energy and electronic applications.