Surface trapping induced negative photoconductivity in Au nanoparticles functionalized SnO2/SnSe2 nanosheets under visible and NIR light

Abstract

In this study, we report negative photoconductivity in SnO2/SnSe2 nanosheets. We synthesized 2D n-type SnSe2 nanosheets by the hydrothermal route and observed highly stable and repeatable negative photoconductivity (NPC) in the presence of both visible (532 nm) and near-infrared (NIR, 905 nm) irradiation. The existence of native SnO2 skin on SnSe2 nanosheets was confirmed with X-ray photoelectron spectroscopy (XPS). Negative photoresponse was improved significantly after Au nanoparticles (∼3.4 nm) functionalization of SnO2/SnSe2 nanosheet. Au-SnO2/SnSe2 exhibited responsivity/detectivity of 47.55 mA/W & 1.49 × 1010 Jones and 47.8 mA/W &1.5 × 1010 Jones at 10 V bias in visible and NIR light intensity of 50 µW/cm2, respectively, and quite a faster fall time of 841 µs and 791 µs in NIR exposure. The origin of NPC in SnSe2 is attributed to the trapping of photogenerated hot carriers by surface adsorption of oxygen in ambient air. The NPC was further increased due to a significant increment of dark current (as well as Idark/Ilight) after Au nanoparticles functionalization on SnO2/SnSe2.