Modeling the optical constants of CuGaSe2 and CuInSe2

The dielectric function data for CuGaSe2 and CuInSe2 have been modeled for both perpendicular (E perpendicular to c) and parallel (E \ \ c) polarizations. We employ the modified Adachi's model dielectric function model with variable broadening. Variable broadening is accomplished by replacing the damping constant Gamma with the energy-dependent expression Gamma (E), where the shape of the broadening function is determined by two adjustable model parameters. In spite of one additional parameter per transition, this model requires fewer parameters than the conventional Adachi's model to achieve equal or better agreement with the experimental data. Our calculations give the relative rms errors for the real and imaginary parts of the index of refraction, delta (n) and delta (k), equal to 0.9% and 9.5% for CuGaSe2 (E perpendicular to c), 0.8% and 7.3% for CuGaSe2 (E \ \ c), 1.1% and 3.0% for CuInSe2 (E perpendicular to c), and 2.5% and 3.7% for CuInSe2 (E \ \ c), respectively.