An ultrafast and self-powered MoS _x Se _{2− x} /Si photodetector with high light-trapping structures and a SiO _x interface layer

MoS_xSe_2-x nanofilms, as a typical metal dichalcogenide, have attracted great interest, due to their adjustable bandgap and distinctive electronic and optical properties. However, the inherent bandgap of MoS_xSe_2-x and the strong interface recombination impede the actualization of a high-sensitivity photodetector (PD). Few-layer MoS_xSe_2-x nanofilms were prepared with vertically orientation at 450 °C, which would be a less restrictive choice of substrates. Herein, a self-powered MoS_xSe_2-x/SiO_x/Si photodetector was fabricated which exhibits unprecedented performance with excellent reproducibility and stability from 405 nm to 980 nm, a high responsivity (0.450 A W^-1), normalized detectivity (4.968 × 10¹² Jones) and ultrafast photoresponse (τ_r = 1.20 μs, τ_f = 4.92 μs) at zero bias under 980 nm incident laser illumination with a density of 200 μW cm^-2. Significantly, the self-powered PD is capable of detecting ultraweak IR signals below 200 μW cm^-2 with high on-off ratios. More importantly, an oxidized atomic layer is generated through the wet oxidation in the Piranha solution. The PD can work well at high frequencies even at 100 kHz, which shows its potential application in high-frequency photoelectric devices and health monitors. Summing up, this work not only suggests that an ultrathin SiO_x interface layer can reduce carrier recombination via simple interface engineering, but also proposes a novel strategy for the preparation of high-performance and low-cost optoelectronic devices.