Understanding metal–semiconductor interfaces is
critical
to the advancement of photocatalysis and sub-bandgap solar energy
harvesting where electrons in the metal can be excited by sub-bandgap
photons and extracted into the semiconductor. In this work, we compare
the electron extraction efficiency across Au/TiO2and titanium
oxynitride (TiON)/TiO2–xinterfaces,
where in the latter case the spontaneously forming oxide layer (TiO2–x) creates a metal–semiconductor
contact. Time-resolved pump–probe spectroscopy is used to study
the electron recombination rates in both cases. Unlike the nanosecond
recombination lifetimes in Au/TiO2, we find a bottleneck
in the electron relaxation in the TiON system, which we explain using
a trap-mediated recombination model. Using this model, we investigate
the tunability of the relaxation dynamics with oxygen content in the
parent film. The optimized film (TiO0.5N0.5)
exhibits the highest carrier extraction efficiency (NFC≈ 2.8 × 1019m–3), slowest trapping, and an appreciable hot electron population reaching
the surface oxide (NHE≈ 1.6 ×
1018m–3). Our results demonstrate the
productive role oxygen can play in enhancing electron harvesting and
prolonging electron lifetimes, providing an optimized metal–semiconductor
interface using only the native oxide of titanium oxynitride.