Abstract
Well-crystallized Sn2S3 semiconductor thin films with a highly (111)-crystallographic orientation were grown using RF sputtering. The surface morphology of the Sn2S3 thin films exhibited a sheet-like feature. The Sn2S3 crystallites with a sheet-like surface had a sharp periphery with a thickness in a nanoscale size, and the crystallite size ranged from approximately 150 to 300 nm. Postannealing the as-synthesized Sn2S3 thin films further in ambient air at 400 °C engendered roughened and oxidized surfaces on the Sn2S3 thin films. Transmission electron microscopy analysis revealed that the surfaces of the Sn2S3 thin films transformed into a SnO2 phase, and well-layered Sn2S3–SnO2 heterostructure thin films were thus formed. The Sn2S3–SnO2 heterostructure thin film exhibited a visible photoassisted room-temperature gas-sensing behavior toward low concentrations of NO2 gases (0.2–2.5 ppm). By contrast, the pure Sn2S3 thin film exhibited an unapparent room-temperature NO2 gas-sensing behavior under illumination. The suitable band alignment at the interface of the Sn2S3–SnO2 heterostructure thin film and rough surface features might explain the visible photoassisted room-temperature NO2 gas-sensing responses of the heterostructure thin film on exposure to NO2 gas at low concentrations in this work.
Highlights
Binary tin sulfide semiconductors, because of their narrow band gap values and n-type semiconducting characteristics, have attracted considerable attention in applications of various photovoltaic and photoactivated devices [1,2,3,4]
A similar sheet-like surface morphology was reported for Sn2S3 thin films synthesized using a chemical solution method [5]
During the gas-sensing process, the electrical resistance increase can be associated with surfacecontrolled processes and explained by the capturing of free electrons from the surfaces of the n-type semiconductors by adsorbed oxidizing NO2 gas molecules [23, 24]. Such adsorbed NO2 gas molecules could capture the electrons from the SnO2 surface of the heterostructure thin film and might have engendered the variation of the depletion layer thickness at the heterointerfaces, resulting in the increased electrical resistance of the sample. This indicated that the higher concentration of electrons on the Conclusions In summary, highly (111)-oriented Sn2S3 semiconductor thin films with a sheet-like surface were grown through RF sputtering
Summary
Because of their narrow band gap values and n-type semiconducting characteristics, have attracted considerable attention in applications of various photovoltaic and photoactivated devices [1,2,3,4]. Tin sulfide semiconductors in the form of a thin-film structure are in high demand. Several synthesis techniques, such as spray pyrolysis [3], thermal evaporation [4], chemical bath deposition [5], and chemical vapor deposition [6], have been successfully employed in preparing tin sulfide semiconductor thin films. Overcoming high barriers is generally necessary for the gas molecules to adsorb onto and desorb from the semiconductor surfaces during gas-sensing response and recovery at low temperatures; fabricating thin-film semiconductor-based gas sensors that have visible gas-sensing behaviors at room temperature remains a considerable challenge. Narrow band gap tin sulfide semiconductors have rarely been reported for applications in gas-sensing materials operated at room temperature. Various heterostructures have been widely investigated and show enhanced functions of the
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