Fig. 1: Schematic and band structure of an encapsulated InSe device.

a, Optical microscope picture of the 3L device with layers highlighted in false colour. FLG, InSe and hBN layers are depicted in grey, violet and blue, respectively. Scale bar, 20 μm. b, Three-dimensional schematic representing an hBN-encapsulated InSe layer with graphene contacts and a wide back gate. The sample is optically excited using a red laser and excitonic species are formed within the semiconductor. When a gate voltage is applied, holes in InSe can tunnel through the bottom hBN giving rise to a tunnelling photocurrent. The electrical measurement scheme is shown on the right. c, Band alignment of the materials of interest in the device of Fig. 1b. Two electron donor (red) and one acceptor (blue) states are induced by the presence of selenium vacancies. d, Band structure of the 3L slab of InSe with a selenium vacancy. A van Hove singularity arises due to the band flattening at the Γ point. e, The DOS in a 3L-InSe shows a sharp peak at the VBM, as well as the donor (red) and acceptor (blue) states. The inset shows in logarithmic scale the region between the highest donor state and the beginning of the conduction band, with its minimum located at 1.54 eV with respect to the acceptor state.