Photodetection in p-n junctions formed by electrolyte-gated transistors of two-dimensional crystals

TL;DR

This paper demonstrates the formation of electrolyte-gated p-n junctions in WSe2 monolayers for photodetection, achieving high responsivity without external bias, advancing optoelectronic applications of 2D materials.

Contribution

It introduces a novel electrolyte-gating technique to create stable p-n junctions in monolayer TMDCs for efficient photodetection.

Findings

Maximum photoresponsivity of 5 mA/W at excitonic resonance

Two-terminal devices outperform three-terminal ones in responsivity

Stable p-n junctions formed at 270 K with electrolyte gating

Abstract

Transition metal dichalcogenide (TMDC) monolayers have attracted much attention due to their strong light absorption and excellent electronic properties. These advantages make this type of two-dimensional crystal a promising one for optoelectronic device applications. In the case of photoelectric conversion devices such as photodetectors and photovoltaic cells, p-n junctions are one of the most important devices. Here, we demonstrate photodetection with WSe2 monolayer films. We prepare the electrolyte-gated ambipolar transistors and electrostatic p-n junctions are formed by the electrolyte-gating technique at 270 K. These p-n junctions are cooled down to fix the ion motion (and p-n junctions) and we observed the reasonable photocurrent spectra without the external bias, indicating the formation of p-n junctions. Very interestingly, two-terminal devices exhibit higher photoresponsivity than that of three-terminal ones, suggesting the formation of highly balanced anion and cation layers. The maximum photoresponsivity reaches 5 mA/W in resonance with the first excitonic peak. Our technique provides important evidence for optoelectronics in atomically thin crystals.