Raman investigations of Cu(In,Ga)Se 2 thin films with various copper contents

Abstract

CuIn 1 − x Ga x Se 2 (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 1 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 1 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 1 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) 3Se 5 or Cu 2(In,Ga) 4Se 7. Cu-rich films with Cu/(Ga + In) > 1 exhibit a non-chalcopyrite mode at 260 cm − 1 which is assigned to Cu 2 − x Se. Mappings of Cu-rich samples revealed a lateral distribution of the Cu 2 − x Se compound in domains of 1–2 μm.