Optical Transitions in RF Sputtered CuIn_xGa_1-xSe₂ Thin Films

Abstract

Thin films of CuIn x Ga 1- x Se 2 were produced over the entire range of 0≤ x ≤1 by rf sputtering. The optical absorption coefficients of the CuIn x Ga 1- x Se 2 thin films were determined from the measured transmittance and reflectance in the wavelength range of 400 to 2000 nm. The optical absorption spectra for sputtered CuIn x Ga 1- x Se 2 thin films ( x ≠0) show three energy gaps, which are attributed to the fundamental edge, and band splitting by crystal-field and spin-orbit splitting, respectively. The primary transition energies exhibit bowing behavior expressed by the relationship E g1 =1.674-0.803 x +0.130 x 2 . The second and third transition energies are 0.06-0.08 eV and 0.22-0.27 eV above the primary transition energies, respectively.