Band Alignment and Composition of the Buried TiO ₂ /GaInP Interface

ABSTRACT Multi‐absorber III–V semiconductors represent the state of the art in high‐efficiency solar‐to‐electricity and solar‐to‐fuel conversion owing to their tunable bandgaps and favorable optoelectronic properties. GaInP is widely used in monolithic tandem devices as a top absorber or charge‐carrier‐selective contact because of its suitable electronic structure. However, GaInP and related III–V materials are prone to photocorrosion under photoelectrochemical (PEC) operation and require protective layers that ensure chemical and electronic passivation. Atomic layer deposition (ALD), particularly plasma‐enhanced ALD (PE‐ALD), enables conformal deposition of films that enhance interfacial stability while maintaining efficient selective charge carrier transport. Here, the band alignment at the GaInP(100)/ interface is examined to determine whether the initial GaInP surface condition–either an atomically well‐defined, phosphorus‐rich surface or a naturally oxidized surface–affects interface formation during mild, low‐power remote oxygen PE‐ALD. Angle‐dependent X‐ray and ultraviolet photoelectron spectroscopy were used to probe the chemical and electronic structure of the buried interfaces. The results show that interface composition and band alignment are largely insensitive to the initial surface condition, with only minor differences in attenuation and interfacial energetics. These findings demonstrate the robustness of mild PE‐ALD for reproducible interface formation and support the design of protected III–V photoelectrodes for PEC applications.