Thickness dependent p-n switching in SnSe2/SnOx/SnSe heterojunction-based NO2 gas sensor as well as photodetector

Abstract

SnSe2/SnOx/SnSe heterojunction thin films with different thicknesses 137, 241 and 297 nm were fabricated via the thermal evaporation technique. XRD, FESEM, Raman spectroscopy, XPS, and U–V visible spectroscopy were used to study the structural, morphological, chemical, and optical properties of the deposited thin films, which revealed that the heterojunction thin films had a microcrystalline structure and a mixed SnSe2, SnSe, SnO, and SnO2 phases. Only the sample with the lower thickness (137 nm) exhibited the p-n type behaviour when concentration (1–5 ppm) and temperature (RT-75 °C) increased. Furthermore, the SnSe2/SnOx/SnSe heterojunction thin-film gas sensor demonstrated good NO2 detecting selectivity. The development of SnSe2/SnOx/SnSe p–n junctions at the thin-film surface may be responsible for the improved NO2-sensing capability of the constructed gas sensor at low operating temperatures. For five ppm NO2, the device response was 151% at RT. Response/recovery times were 134/494 s, respectively. The estimated detection limit (LOD) was 515 ppb. NO2 gas had a higher response than SO2, NO, H2S, CO, H2, C2H5OH, and NH3. The mechanism of concentration, temperature-dependent p–n switching, selective detection of NO2 at RT, and complete response and recovery have been deliberated based on physisorption and charge transfer. The lower thickness (137 nm) sample exhibits good photo response in visible light with power (32 mW). It has good responsivity, detectivity and external quantum efficiency. This research will give 2D materials a new dimension of selective gas sensors and photodetection at room temperature.

Keywords

• SnSe2/SnOx/SnSe heterojunction
• Fast response
• Room-temperature NO2 gas sensor
• High selectivity
• p–n transition