Raman investigations of Cu(In,Ga)Se2 thin films with various copper contents

CuIn1-xGaxSe2 (CIGS) thin films with a Ga/(Ga+In) ratio x=0.3 with various Cu contents were characterized by micro-Raman spectroscopy. All samples were investigated with a frequency-doubled Nd:YAG laser (532 nm) in the back-scattering geometry. The frequency of the CIGS Raman A, mode decreases with increasing Cu content and reaches a minimum at a composition near stoichiometry. Furthermore, the full width at half maximum of the A, mode decreases with increasing Cu content of the CIGS thin films due to better crystallinity and reduced disorder in the films. In addition to the CIGS A, mode, CIGS with Cu/(Ga+In) 0.8 showed a broad shoulder at around 150 cm(-1) which is a result of ordered defect compounds like Cu(In,Ga)(3)Se-5 or Cu-2(In,Ga)(4)Se-7. Cu-rich films with Cu/(Ga+In) >1 exhibit a non-chalcopyrite mode at 260 cm(-1) which is assigned to Cu2-xSe. Mappings of Cu-rich samples revealed a lateral distribution of the Cu2-xSe compound in domains of 1-2 mu m. (C) 2008 Elsevier B.V. All rights reserved.