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.