Ultrafast Electron Dynamics at the P‐rich Indium Phosphide/TiO₂ Interface

<jats:title>Abstract</jats:title><jats:p>The current efficiency records for generating green hydrogen via solar water splitting are held by indium phosphide (InP)‐based photo‐absorbers, protected by TiO<jats:sub>2</jats:sub> layers grown through atomic layer deposition (ALD). InP is also a leading material for photonic integrated circuits and computing, where ultrafast near‐surface behavior is key. A previous study described electronic pathways at the phosphorus‐rich (P‐rich) surface of p‐doped InP(100) using time‐resolved two‐photon photoemission (tr‐2PPE) spectroscopy. Here, the intricate electron pathways of the P‐rich InP surface modified with ALD‐deposited TiO<jats:sub>2</jats:sub> are explored. Photoexcited bulk InP electrons migrate through a bulk‐to‐surface transition cluster of states and surface states and inject into the TiO<jats:sub>2</jats:sub> conduction band (CB). Energy levels and occupation dynamics of CB states in P‐rich InP and TiO<jats:sub>2</jats:sub> adlayers are observed, with discrete states preserved up to 10 nm TiO<jats:sub>2</jats:sub> deposition. Thermalization lifetimes of excited electrons &gt; 0.8 eV above the InP conduction band minimum (CBM) are preserved for layer thicknesses up to 2.5 nm. Annealing at 300 °C to achieve crystalline TiO<jats:sub>2</jats:sub> reconstructions destroys interfacial states, affecting charge transfer. These observations enable innovative engineering of the P‐rich InP/TiO<jats:sub>2</jats:sub> heterointerface, opening new possibilities for studying hot‐carrier extraction, adsorbate effects, surface plasmons, and improving photovoltaic and PEC water‐splitting devices.</jats:p>