Impact of Oxygen Adsorption on GeSn: A Consideration of Oxygen Diffusion and Optical–Electrical Properties

Germanium-tin (GeSn) alloys are promising materials for application in photocatalysis and chemical catalysis due to their tunable band structure and efficient light absorption. Surface interactions, particularly oxygen adsorption, can significantly influence electronic structure, charge transfer, and catalytic efficiency. This study investigates the effects of oxygen adsorption and diffusion on GeSn surfaces, focusing on the consequent impact on light absorption, reflection, and refractive index. The results reveal that oxygen preferentially adsorbs near Sn sites with chemisorption energy minimum of -0.9 eV, inducing localized electronic states and charge redistribution, which alter the catalytically active sites. Oxygen adsorption reduces light absorption by 10-15% at the ultraviolet to visible light range, resulting in a red-shift in the absorption edge, enhancing light scattering via surface dipoles, particularly in the monolayer due to the higher associated surface-to-volume ratio. The findings of this study provide critical insight into oxygen-modulated electronic and optical properties, which can inform strategies to optimize GeSn-based materials for solar energy conversion and catalytic applications.