Formation of All Tin Oxide p–n Junctions (SnO–SnO₂) during Thermal Oxidation of Thin Sn Films

Abstract

Metastable stannous oxide (SnO) phase of p‐type semiconductor and all tin oxides p–n junctions of SnO–SnO2 nanostructures are formed by controlled thermal oxidation of thin tin films. High purity Sn is deposited on quartz substrates using a vacuum‐assisted thermal evaporation technique. Afterwards, controlled thermal oxidation at different temperatures is performed in air ambient condition (150–800 °C). Various surface characterization techniques have been employed to analyze the structure, morphology, chemistry, optical, and electronic properties of these SnOx films. P‐type SnO phase is found to be thermodynamically stable at lower oxidation temperatures (250–400 °C), while n‐type SnO2 phase starts to appear above 500 °C. Highly uniform and dense SnO nanospheres along with few 1D nanorods are observed after oxidation at 400 °C. Mixed oxide phases of p–n junctions with a sudden decrease in electrical conductivity is observed for 500 °C film. Significantly lower surface conductivity of mixed oxide phase indicates the formation of depletion layers between p‐type SnO and n‐type SnO2 nanograins. A transition from SnO layer to SnO2 layer is also observed above 600 °C. Overall, SnOx‐based nanostructures would be a potential candidate for solar cells, p‐channel thin film transistors, p–n junction diodes and gas sensors.