Effect of structural phase transformations under pressure on electronic and optical properties of CuInS2

Abstract

First-principles plane-wave calculations were employed to study the phase transitions, electronic and optical properties of chalcopyrite CuInS2 (CIS) under pressure, which is a promising semiconductor compound material for nonlinear optical, photovoltaic and bio-applications. From the variations of Gibbs free energy and volume with pressure, we confirmed an experimentally found phase transformation of CIS from tetragonal I4¯2d structure into the cubic Fm3¯m phase. It occurs at 7.9 GPa with a volume reduction of 15.6%, which are comparable with the experimental values of 9.5 GPa and 12%. A new possible phase transition of CIS from the cubic Fm3¯m structure to the orthorhombic Cmcm structure under higher pressure was predicted occurring at 49.6 GPa with a volume reduction about 0.64%. Using the more accurate HSE06 functional, we found that the growth rate of energy gap with pressure (dEg/dP) for the I4¯2d phase is about 24.8 meV/GPa, very close to the experimental value of 24 meV/GPa. The calculated electronic properties for Fm3¯m and Cmcm phases show that CIS is a metallic material under high pressure, rather than a semiconductor. The optical absorption spectra indicate that with the increase of pressure the absorption edge of CIS becomes smaller while the optical energy gap is larger.