摘要： InP is among the most studied materials for energy-conversion applications including optoelectronics and photoelectrochemical devices. One of the longstanding challenges with this material—and III-V semiconductors more generally—is to understand and control surface oxide formation, which critically impacts device functionality, performance and durability. We integrate advanced in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and ab initio simulations to reveal the mechanism of the oxidation process on InP(001) surface. By interpreting the APXPS results through direct ab initio spectroscopic calculations of surface models, and by comparing calculated and measured work functions, we provide an unbiased picture of the chemical evolution of the thermal oxide. At low temperatures (< 573 K), O2 exposure leads to predominant formation of crosslinked POx units dispersed with submonolayer thickness, which grow into an amorphous 2D film that is kinetically limited to the surface layer. Increased temperature (> 573 K) leads to the polymerization of POx units and the formation of a complex, inhomogeneous 3D network of surface oxide that is progressively indium rich and phosphorus poor towards the surface. Finally, accelerated phosphorus loss via a hitherto unreported coupled charge-transfer isomer transformation mechanism leads to the formation of a thick, amorphous In2O3-like oxide at 773 K with very different optoelectronic and hot carrier transportation properties. In addition to unraveling complex mechanisms of surface oxidation, our results suggest the possibility of deliberately tuning oxide composition by leveraging competition between thermodynamic and kinetic factors.