Quasiparticle, optical, and excitonic properties of layer dependent GaSe

The two-dimensional (2D) optical absorbance and complex optical conductivity can well define the optical properties of 2D materials and they are fundamental for the design and manufacture of optoelectronic devices. In this work, quasiparticle electronic structure, optical absorbance and complex optical conductivity of 1-layer to 3-layer GaSe are studied by the self-energy GW0 method and the Bethe–Salpeter equation (BSE). Relative to bulk GaSe with a direct bandgap, our calculation results show that three kinds of two-dimensional GaSe are all quasi-direct band gap semiconductors. Due to the exciton effect, their optical absorbance spectrums are red-shifted, and the absorption intensity increases rapidly near the band gap. The exciton binding energies of 1-layer to 3-layer GaSe are increased significantly with respect to bulk GaSe. •Considering the vacuum layer effect, quasiparticle electronic structure, optical absorbance and complex optical conductivity of 2D GaSe from a single layer to three layers are studied by many-body GW method and the Bethe–Salpeter equation (BSE).•GaSe of 1 L–3 L are quasi-direct bandgap semiconductors with 4.15 eV, 3.33 eV, and 2.88 eV bandgap, respectively.•The calculated results of 2D absorbance show that the layered GaSe has a strong exciton effect, and the exciton effect leads to a large increase in the absorbance.•The imaginary parts of the complex optical conductivities for 1 L–3 L GaSe are negative in the energy range of 0 to about 5.1 eV, which can be used to design and manufacture metamaterials and sensors.