Fundamental and optical band gaps of layered In₂Se₃

Indium selenide is a promising material for photodetectors due to the highly efficient absorption, fast response, and high sensitivity extending into ultraviolet, visible, and near-infrared spectral regions. Despite these promising properties, the reports on the electronic structure and the values for the direct vs. indirect band gaps of In₂Se₃ remain quite controversial, with results varying in a wide range, from 0.7 to 1.4 eV. Using hybrid density functional calculations, we investigated the electronic and optical properties of layered phases of In₂Se₃: α phase (space group R3m), β phase (space group R-3m), and δ phase (space group P-3m1). We report fundamental and optical band gaps for the three phases, the real and imaginary dielectric functions, and absorption coefficients. The results are then discussed in the light of available experimental data.