High photosensitivity and broad spectral response of multi-layered germanium sulfide transistors

In this paper, we report the optoelectronic properties of multi-layered GeS nanosheet (∼28 nm thick)-based field-effect transistors (called GeS-FETs). The multi-layered GeS-FETs exhibit remarkably high photoresponsivity of Rλ ∼ 206 A W−1 under 1.5 μW cm−2 illumination at λ = 633 nm, Vg = 0 V, and Vds = 10 V. The obtained Rλ ∼ 206 A W−1 is excellent as compared with a GeS nanoribbon-based and the other family members of group IV–VI-based photodetectors in the layered-materials realm, such as GeSe and SnS2. The gate-dependent photoresponsivity of GeS-FETs was further measured to be able to reach Rλ ∼ 655 A W−1 operated at Vg = −80 V. Moreover, the multi-layered GeS photodetector holds high external quantum efficiency (EQE ∼ 4.0 × 104%) and specific detectivity (D* ∼ 2.35 × 1013 Jones). The measured D* is comparable to those of the advanced commercial Si- and InGaAs-based photodiodes. The GeS photodetector also shows an excellent long-term photoswitching stability over a long period of operation (>1 h). These extraordinary properties of high photocurrent generation, broad spectral range, and long-term stability make the GeS-FET photodetector a highly qualified candidate for future optoelectronic applications.