Effect of pressure on direct optical transitions of γ-InSe

Abstract

We have investigated the effect of hydrostatic pressure on direct optical transitions of the layered semiconductor γ-InSe by photoreflectance (PR) spectroscopy (T = 300 K). In addition, electro-reflectance (ER) measurements were performed at ambient pressure. Six structures are resolved in the ER spectra in the energy range from 1.1 to 3.6 eV. The pressure dependence of four of these structures was determined by PR spectroscopy for pressures up to 8 GPa. In order to assign the features observed above the fundamental gap we have carried out band structure calculations for InSe at ambient pressure using a full-potential linear augmented plane wave method. Based on calculated band gap deformation potentials for different uniaxial strains, we explain the strongly nonlinear pressure dependence of the fundamental band gap and the absence of such effects for the higher lying transitions which increase almost linearly with pressure.