Fundamental absorption edge in CuIn5Se8 and CuGa3Se5 single crystals

Abstract

Optical absorption spectra of CuIn5Se8 and CuGa3Se5 single crystals have been investigated. The energy gap E g for CuIn5Se8 (CuGa3Se5) was found to be varied from 1.27 (1.79) to 1.21 (1.71) eV in the temperature range between 10 and 300 K. The temperature dependence of E g was studied by means of the Einstein model and the Pässler model. The Einstein temperature {222 (267) K}, the Debye temperature {310 (380) K}, a dimensionless constant related to the electron–phonon coupling {1.62 (2.65)} as well as an effective energy {20 (24) meV} and a cut-off phonon energy {35 (39) meV} have been estimated for CuIn5Se8 (CuGa3Se5). It was also found that the major contribution of phonons to the shift of E g versus temperature in CuIn5Se8 (CuGa3Se5) is mainly from optical phonons.