Composition and Resulting Band Alignment at the TiO ₂ /InP Heterointerface: A Fundamental Study Combining Photoemission Spectroscopy and Theory

Abstract The composition and resulting band alignment at the TiO 2 /InP heterointerface are critical for optimizing semiconductor‐based photoelectrochemical and photovoltaic devices. Hence, a systematic investigation of the chemical composition and electronic properties of TiO 2 film grown via atomic layer deposition (ALD) on p‐doped, atomically well‐ordered, phosphorus‐terminated InP(100) surfaces is conducted. A combination of UV and X‐ray photoelectron spectroscopy with ab initio molecular dynamics simulations is applied to provide a comprehensive atomic‐scale understanding of the heterointerface. These results reveal that the P−P dimers in the first monolayer remain intact during the initial ALD cycles, while oxygen preferentially binds between indium in the second monolayer and phosphorus in the first monolayer, leading to the formation of interfacial indium phosphate (InPO x ) species. The presence of chlorine residues from the TiCl 4 precursor persists throughout the deposition process and influences the chemical environment of the interface. Band alignment analysis confirms the formation of a type‐II heterojunction, characterized by a valence band offset of approximately 2.3 eV and a conduction band offset of 0.45 eV, facilitating charge carrier separation essential for high‐efficiency photoelectrochemical applications. These detailed insights into the interfacial chemistry and electronic structure are fundamental to advance the development of efficient semiconductor‐based energy conversion devices.