Nano Lett. 13, 1649–1654 (2013)

Ultrathin, two-dimensional nanomaterials are highly promising for fabricating miniature electronic and optoelectronic devices. For example, graphene is potentially attractive for creating wideband, high-speed photodetectors, but it suffers from low responsivity, a very low external quantum efficiency and no spectral selectivity. This has led researchers to investigate two-dimensional nanostructures made from other materials. Now, PingAn Hu and co-workers from China, the USA and Japan have fabricated highly responsive photodetectors consisting of GaS nanosheets on both rigid (SiO2/Si) and flexible (polyethylene terephthalate) substrates. They report a photoresponsivity of 4.2 A W−1 and an external quantum efficiency of 9,370% at 254 nm for GaS nanosheets on flexible substrates, which are several orders of magnitude higher than those of pristine graphene. Furthermore, these devices have high linear dynamic ranges of 97.7 dB and 78.73 dB on rigid and flexible substrates, respectively, which are higher than those of currently used InGaAs photodetectors. Theoretical analysis of the electronic band structures suggests that the photoresponse of GaS nanosheets is enhanced relative to that of bulk GaS by the existence of a double peak in the valence band and a reduction in the effective electron mass with decreasing layer thickness. The findings indicate that two-dimensional GaS nanostructures are highly suitable for realizing high-performance photodetectors on a variety of substrates.