Defect-Driven Luminescence and Surface Stability in ScN Thin Films: A Combined Thermally Stimulated Study

This study examines the relationship between the microstructure and surface emission properties of scandium nitride (ScN) thin films, a promising material for thermoelectric applications. ScN layers were deposited on MgO (001) substrates at two different temperatures, 700 and 800 °C, to control defect levels and crystalline quality. Structural analysis using X-ray diffraction and atomic force microscopy showed that the 700 °C film had poorer crystallinity, multiple orientations, a higher density of twin domains, and a rough surface with pyramidal-shaped crystals. In contrast, the 800 °C film demonstrated better epitaxial quality, a dominant 002 texture, and a much smoother surface. We performed simultaneous measurements of thermally stimulated luminescence (TSL), thermally stimulated exo-electron emission (TSEE), and thermally stimulated desorption (TSD) under ultrahigh vacuum conditions to analyze surface processes. TSEE revealed minimal or no electron emission, suggesting that the rougher 700 °C film acts like a p-type material, likely due to scandium vacancies. TSD results indicated that the rougher 700 °C film experienced greater desorption of ScO2 and Sc(OH)3 radicals at lower temperatures, confirming weaker surface bonding compared to the more compact 800 °C film. Most notably, the TSL intensity for the 700 °C film was about ten times higher than for the 800 °C film, with the peak at a lower temperature (Tm= 20 °C vs 101 °C). This temperature dependence, along with kinetic analysis (second-order for 700 °C and first-order for 800 °C), shows that increased surface roughness and defect levels─especially Sc vacancies─lower the activation energy needed for light emission, highlighting a direct link between structure and properties in luminescent materials engineering.