Understanding CIGS Device Performances Through Photoreflectance Spectroscopy

Cu (In1-x,Ga-x) S-2 was studied using photoreflectance spectroscopy. In this study, efforts are devoted to optimizing PR set-up for measuring CIGS grown by electrodeposition: issues such as photoluminescence perturbation, high roughness and scattering are addressed. Dual frequency photoreflectance, where both probe and pump beams are modulated, is proposed here to over come the poor signal to noise ratio. Considering the low electric field regime, material parameters are extracted by employing the third derivative functional form of dielectric functions to fit data.The reliability of the technique is finally tested by measuring PR spectra on a specific 15 x 15cm(2) wafer and explanations of PR line-shape evolution on this wafer are discusse.