High-responsivity broad-band sensing and photoconduction mechanism in direct-Gap α-InSe nanosheet photodetectors.

Photoconductivities (PCs) with high responsivity in two-dimensional (2D) diindium triselenide (InSe) nanostructures with α-phase hexagonal structure were studied. The InSe nanosheet photodetectors fabricated by focused-ion beam technique exhibit broad spectral response with wavelength range from 300 nm to 1000 nm. The InSe nanosheets achieve optimal responsivity of 720 A W in near-infrared region (808 nm), and detectivity of 2.2 × 10 Jones, which were higher than several 2D material photodetectors. The physical origins that result in high photoresponse in InSe nanosheets such as carrier lifetime and mobility were also characterized by time-resolved PC and field-effect transistor measurements. The fast (hundred microseconds to milliseconds) and slow (seconds and longer) current rise or decay processes were both observed during the photoresponse. The narrowing (or relaxation) of depletion region and oxygen-sensitized photoconduction mechanism were suggested to be the causes of the efficient photoresponse in the InSe nanostructure detectors. All these observations suggest that α-InSe nanosheets could be a promising candidate for photosensitive material applications.