Scanning photocurrent microscopy reveals electron-hole asymmetry in ionic liquid-gated WS2 transistors

TL;DR

This study uses scanning photocurrent microscopy to investigate electron-hole asymmetry in ionic liquid-gated WS2 transistors, revealing differences in minority carrier diffusion lengths under different doping conditions.

Contribution

It demonstrates the ability to invert photocurrent sign via gate bias and compares minority carrier diffusion lengths, highlighting electron-hole asymmetry in WS2.

Findings

Minority carrier diffusion length is larger in hole accumulation than in electron accumulation.

Photocurrent decay follows an exponential trend consistent with Schottky barrier models.

Electron-hole asymmetry is observed in the diffusion properties of WS2.

Abstract

We perform scanning photocurrent microscopy on WS2 ionic liquid-gated field effect transistors exhibiting high-quality ambipolar transport. By properly biasing the gate electrode we can invert the sign of the photocurrent showing that the minority photocarriers are either electrons or holes. Both in the electron- and the hole-doping regimes the photocurrent decays exponentially as a function of the distance between the illumination spot and the nearest contact, in agreement with a two-terminal Schottky-barrier device model. This allows us to compare the value and the doping dependence of the diffusion length of the minority electrons and holes on a same sample. Interestingly, the diffusion length of the minority carriers is several times larger in the hole accumulation regime than in the electron accumulation regime, pointing out an electron-hole asymmetry in WS2.