Optimizing Hot Electron Harvesting at Planar Metal-Semiconductor Interfaces with Titanium Oxynitride Thin Films.

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/TiO 2 and titanium oxynitride (TiON)/TiO 2- x interfaces, where in the latter case the spontaneously forming oxide layer (TiO 2- 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/TiO 2 , 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 (TiO 0.5 N 0.5 ) exhibits the highest carrier extraction efficiency ( N FC ≈ 2.8 × 10 19 m -3 ), slowest trapping, and an appreciable hot electron population reaching the surface oxide ( N HE ≈ 1.6 × 10 18 m -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.