Surface photovoltaic effect and electronic structure of β -InSe

Using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of β-InSe, a van der Waals semiconductor with a direct band gap. Our measurements show a good agreement with ab initio calculations, which helps reveal the important impact of spin-orbit coupling on the electronic structure of β-InSe. Using surface potassium doping, we tune the chemical potential of the system and observe the unoccupied conduction band. The direct band gap is determined to be about 1.3 eV. Interestingly, we observe a global band shift when the sample is illuminated by a continuous-wave laser at 632.8 nm, which can be understood by an efficient surface photovoltaic effect. The surface photovoltaic can be tuned by in situ surface potassium doping. Our results not only provide important insights into the semiconducting properties of InSe, but also suggest a feasible method to study and engineer the surface photovoltaic effect in InSe-based devices.