  We present a comprehensive study of the electronic structure of the layered
semiconductor InSe using density functional theory. We calculate the band
structure of the monolayer and bulk material with the band gap corrected using
hybrid functionals. The band gap of the monolayer is 2.4 eV. The band edge
states are surprising isotropic. The electron affinities and band offsets are
then calculated for heterostructures as would be used in tunnel field effect
transistors (TFETs). The ionization potential of InSe is quite large, similar
to that of HfSe2 or SnSe2, and so InSe is suitable to act as the drain in the
TFET. The intrinsic defects are then calculated. For Se-rich layers, the Se
adatom is the lowest energy defect, whereas for In-rich layers, the In adatom
is most stable for Fermi energies across most of the gap. Both substitutional
donors and acceptors are calculated to be shallow, and not reconstructed.
Finally, the Schottky barriers of metals are found to be strongly pinned, with
the Fermi level pinned by metal induced gap states about 0.5 eV above the
valence band edge.
