Electrical control of neutral and charged excitons in few-layer InSe

Indium selenide(InSe), a layered metal chalcogenide semiconductor with a layer dependent band structure, high electron mobility and strong light-matter interaction, has gained considerable interests as a promising material system for optoelectronics applications. Monolayer InSe is predicted to be an indirect band gap material. However, few-layer InSe maintains direct band gap optical properties and enables electrostatic gating. Here we report the observation of the electrical field controlled neutral and charged excitons in high-quality hBN encapsulated few-layer InSe devices. Near the charge neutrality point, the photoluminescence (PL) spectra display a strong and narrow peak with 4meV linewidth (at 20K) associated with the recombination of neutral excitons. By adjusting the Fermi energy, we can tune the PL emission so that the PL spectra are dominated either by positively charged or negatively charged trions. We found relatively large trion binding energies of about 8meV, which further indicates the potential of few-layer InSe for optoelectronics.