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

Understanding metal-semiconductor interfaces iscriticalto the advancement of photocatalysis and sub-bandgap solar energyharvesting where electrons in the metal can be excited by sub-bandgapphotons and extracted into the semiconductor. In this work, we comparethe electron extraction efficiency across Au/TiO2 and titaniumoxynitride (TiON)/TiO2-x interfaces,where in the latter case the spontaneously forming oxide layer (TiO2-x ) creates a metal-semiconductorcontact. Time-resolved pump-probe spectroscopy is used to studythe electron recombination rates in both cases. Unlike the nanosecondrecombination lifetimes in Au/TiO2, we find a bottleneckin the electron relaxation in the TiON system, which we explain usinga trap-mediated recombination model. Using this model, we investigatethe tunability of the relaxation dynamics with oxygen content in theparent film. The optimized film (TiO0.5N0.5)exhibits the highest carrier extraction efficiency (N (FC) approximate to 2.8 x 10(19) m(-3)), slowest trapping, and an appreciable hot electron population reachingthe surface oxide (N (HE) approximate to 1.6 x10(18) m(-3)). Our results demonstrate theproductive role oxygen can play in enhancing electron harvesting andprolonging electron lifetimes, providing an optimized metal-semiconductorinterface using only the native oxide of titanium oxynitride.