Surface Oxide Characterization and Interface Evolution in Atomic Layer Deposition of Al 2 O 3 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 P═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 Al 2 O 3, 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/(NH 4 ) 2 S] 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 2 O 3 is slower on the HF/(NH 4 ) 2 S-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.