Intrinsic Photoresponses of As-Exfoliated Few-Layer MoS2 Phototransistors

The photoresponse of two-dimensional MoS2 photodetectors is often dominated by extrinsic effects, such as photoinduced Schottky barrier modulation and interfacial trap-induced photogating, which obscure the intrinsic material properties. To investigate the channel-dominated photoresponse of as-exfoliated few-layer MoS2, we fabricate suspended-channel phototransistors with bismuth-based Ohmic contacts to suppress major extrinsic effects from contacts and substrate interfaces. Through a direct comparison with conventional substrate-supported devices also with Ohmic contacts, we demonstrate that the suspended devices exhibit a fast response (45/83 μs rise/fall time) and a low-noise photocurrent consistent with a photoinduced narrowing of local depletion regions associated with defect states, described by a depletion-region modulation model originally developed for polycrystalline photoconductors. In contrast, conventional devices show orders-of-magnitude higher responsivity but suffer from slow, trap-dominated dynamics and significantly elevated noise. Parameter extraction from the photocurrent fitting reveals a minority carrier recombination lifetime of ∼2.03 ns in the suspended channel. This work clarifies the intrinsic photoresponse mechanism of MoS2 and underscores the critical role of interface engineering in realizing high-speed, low-noise photodetectors based on two-dimensional semiconductors.