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.
@article{arxiv.1611.01589,
title = {Photodetection in p-n junctions formed by electrolyte-gated transistors of two-dimensional crystals},
author = {Daichi Kozawa and Jiang Pu and Ryo Shimizu and Shota Kimura and Ming-Hui Chiu and Keiichiro Matsuki and Yoshifumi Wada and Tomo Sakanoue and Yoshihiro Iwasa and Lain-Jong Li and Taishi Takenobu},
journal= {arXiv preprint arXiv:1611.01589},
year = {2016}
}