Surface oxide characterization and interface evolution in atomic layer deposition of Al₂O₃ on InP(100) studied by in situ infrared spectroscopy

Combined in situ IR measurements and first-principles calculations of InP(100) surfaces reveal that mild annealing (∼300 C), typically needed for atomic layer deposition, leads to the formation of InP-derived surface hydrophosphate species (both Pî - O and P-OH sites). The initial interaction of trimethylaluminum at 300 C results in the formation of P-O-Al linkages through covalent and dative bonding by reaction with surface hydroxyls. During subsequent ALD cycles to deposit Al₂O₃, an interfacial layer composed of P-O-Al bonds (1140 cm^-1) is formed, requiring approximately seven cycles for completion. Similar chemical transformations are observed on hydrofluoric acid and ammonium-sulfide treated [HF/(NH₄)₂S] surfaces but to a lesser degree since the oxide thickness is reduced, requiring only approximately three cycles to fully complete the interfacial layer. Initially, the ALD growth of Al ₂O₃ is slower on the HF/(NH₄) ₂S-treated InP(100) surface than on the native oxide surface due to a lower density of hydroxyl groups. However, this slow growth leads to a denser film, highlighting the importance of the chemical composition of the initial InP(100) substrate.