Environmental stability and ageing of ScN thin films from XPS Ar+ depth profiling

Abstract

A basic knowledge on chemical stability and reactivity of a wide band gap ScN semiconductor in the presence of air atmosphere, where O2 and H2O represent the main degradation or corrosive agents, is of vital importance for a long-term performance of ScN-based devices for thermoelectric applications. Here, we present a systematic XPS Ar+ depth profiling analysis and optical and TEM characterizations of naturally room temperature air-aged thin ScN films prepared by a high-temperature DC sputtering on MgO(0 0 1) and SiO2 substrates. We find that superior crystalline quality ScN/MgO films degrade weakly after their quick initial surface oxidation and/or hydrolysis. Their oxidation is rather local and associated with the film-penetrating void-like interfaces. Significant initial surface oxidation and subsequent bulk oxidation after ageing is, however, observed for polycrystalline ScN/SiO2 films. Ab initio calculations of pure ScN and ScN with diluted nitrogen vacancies and/or substitutional oxygen impurities, which assist our experimental research, reveal pronounced impact of these defects on the ScN electronic structure. The modeled compositions reflect homogeneously and weakly oxidized films, while the real films correspond to relatively pure ScN crystallites with interfaces rich in oxygen.