Bandgap tunable preparation of GaS nanosheets and their application in photoelectrochemical photodetectors

Bandgap engineering of two-dimensional (2D) materials is essential for the design of photoelectrochemical (PEC) devices. Gallium(II) sulfide (GaS), a layered semiconductor material with a direct bandgap of approximately 3.05 eV, has recently gained extensive attention owing to its unique photoresponse property. However, its bandgap tunability relative to the number of layers has not been experimentally confirmed; thus, the effect of bandgap on the photoresponse has not been explored yet. Herein, few-layered GaS nanosheets (Ns) are prepared using a simple liquid-phase exfoliation (LPE) approach. After centrifuging at different speeds, GaS Ns with defined layers are obtained, which enable verification of the tunable bandgap from 2.02 to 3.15 eV. When applied as a PEC-type photodetector, the responsivity of the photodetector is 4.77 mA W⁻¹ and 33.7 μA W⁻¹ under bias voltages of 0.6 and 0 V, respectively. Theoretical models of the electronic structure suggest that a reduction in the number of layers, leading to a decrease of the effective mass at the valence band maximum (VBM), can enhance the carrier mobility of GaS Ns. This results in high photocurrents and indicates that 2D GaS Ns are ideal materials for future high-performance optoelectronic systems.