Elucidating the Photoresponse of Ultrathin MoS₂ Field-Effect Transistors by Scanning Photocurrent Microscopy

The mechanisms underlying the intrinsic photoresponse of few-layer (FL) molybdenum disulfide (MoS₂) field-effect transistors are investigated via scanning photocurrent microscopy. We attribute the locally enhanced photocurrent to band-bending-assisted separation of photoexcited carriers at the MoS₂/Au interface. The wavelength-dependent photocurrents of FL MoS₂ transistors qualitatively follow the optical absorption spectra of MoS₂, providing direct evidence of interband photoexcitation. Time and spectrally resolved photocurrent measurements at varying external electric fields and carrier concentrations establish that drift-diffusion currents dominate photothermoelectric currents in devices under bias

Investigation of Band-Offsets at Monolayer–Multilayer MoS₂ Junctions by Scanning Photocurrent Microscopy

The thickness-dependent band structure of MoS₂ implies that discontinuities in energy bands exist at the interface of monolayer (1L) and multilayer (ML) thin films. The characteristics of such heterojunctions are analyzed here using current versus voltage measurements, scanning photocurrent microscopy, and finite element simulations of charge carrier transport. Rectifying <i>I</i>–<i>V</i> curves are consistently observed between contacts on opposite sides of 1L/ML junctions, and a strong bias-dependent photocurrent is observed at the junction. Finite element device simulations with varying carrier concentrations and electron affinities show that a type II band alignment at single layer/multilayer junctions reproduces both the rectifying electrical characteristics and the photocurrent response under bias. However, the zero-bias junction photocurrent and its energy dependence are not explained by conventional photovoltaic and photothermoelectric mechanisms, indicating the contributions of hot carriers