Optimizing hot electron harvesting at planar metal-semiconductor interfaces with titanium oxynitride thin films

TL;DR

This study compares electron extraction at metal-semiconductor interfaces, demonstrating that titanium oxynitride films with optimized oxygen content improve hot electron harvesting and prolong electron lifetimes compared to traditional gold contacts.

Contribution

The paper introduces a trap-mediated recombination model for titanium oxynitride interfaces and shows how oxygen content tuning enhances electron harvesting efficiency.

Findings

Titanium oxynitride with specific oxygen content outperforms gold in electron extraction.

Optimized TiO0.5N0.5 film shows highest carrier extraction and longest electron lifetimes.

Oxygen plays a key role in enhancing and prolonging hot electron populations.

Abstract

Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where sub-bandgap photons can be excited and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO2 and titanium oxynitride/TiO2-x interfaces, 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, slowest trapping and an appreciable hot electron population reaching the surface oxide. Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and elongating electron lifetimes providing an optimized metal-semiconductor interface using only the native oxide of titanium oxynitride.