Fig. 5

Raman and optical characterisation of the Se-only and Se+Na2Se samples. a Raman spectra (532 nm) of the back sides of Se-only and Se+Na2Se films after lift-off and b corresponding photoluminescence spectra (dotted curves, room temperature, 16 mW laser power). The GGI dependence of the A1 Raman frequencies of CuInSe2, CuGaSe242, CuIn3Se5 and CuGa3Se545 are shown as dashed vertical lines in a. The solid curves in b are the optical absorption spectra obtained by illumination from the front surfaces through the CIS/GaAs samples