Elucidating the photoresponse of ultrathin MoS2 field-effect transistors by scanning photocurrent microscopy

TL;DR

This study uses scanning photocurrent microscopy to investigate the intrinsic photoresponse mechanisms of ultrathin MoS2 transistors, revealing band-bending effects, interband excitation, and the dominance of drift-diffusion currents under bias.

Contribution

It provides new insights into the photoresponse mechanisms of few-layer MoS2 transistors, highlighting the roles of band-bending and drift-diffusion currents, which were not fully understood before.

Findings

Photocurrent enhancement at the MoS2/Au interface due to band-bending.

Photocurrent spectra follow MoS2 absorption spectra, indicating interband excitation.

Drift-diffusion currents dominate over photothermoelectric currents under bias.

Abstract

The mechanisms underlying the intrinsic photoresponse of few-layer (FL) molybdenum disulphide (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 few layer 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.