First-Principles Study of Dominant Surface Terminations on BaSnO₃ (001) Surface: Implications for Precise Control of Semiconductor Thin Films

BaSnO 3 thin films have attracted significant attention due to their exceptional properties, specifically high electron mobility at room temperature, for optoelectronic applications, such as pn diodes and field-effect transistors. However, the dominant surface terminations of these films, particularly their dependence on growth conditions and water leaching, remain elusive. Here, we studied the impacts of growth conditions and water leaching on the dominant surface terminations of BaSnO 3 thin films by modeling oxygen vacancies and water adsorption using first-principles calculations. Our calculations show that, in the BaSnO 3 model without oxygen vacancies (corresponding to an oxygen-rich condition), the required cleavage energy to remove the surface SnO 2 (BaO·H 2 O) layer is lower than that required to remove the BaO (SnO 2 ·H 2 O) layer. This implies that BaSnO 3 thin films subjected to O 2 annealing display a Ba-excess surface without H 2 O leaching, whereas they have a Sn-excess surface with H 2 O leaching. In contrast, the calculated results for the BaSnO 3 model with oxygen vacancies (corresponding to an oxygen-deficient condition) show that the required cleavage energy to remove the surface SnO 2 (SnO 2 ·H 2 O) layer is less than that required to remove the BaO (BaO·H 2 O) layer, suggesting that BaSnO 3 thin films prepared under oxygen-deficient conditions should exhibit Ba-excess surfaces regardless of H 2 O leaching. This study offers useful insights into achieving precise control over the surface properties of BaSnO 3 films.