Mapping of gradient composition CuxGaySe2 film properties using Raman and PL-spectroscopy

Detailed Raman studies were conducted for the structural characterization of CuxGaySe2 films grown using physical vapour deposition. CuxGaySe2 gradient composition samples were mapped using Raman spectroscopy in combination with photoluminescence (PL) and energy dispersive x-ray spectroscopy. The Raman spectra recorded under excitation with near band gap laser light have a high signal-to-noise ratio and can be used to study the film structure. In particular, composition dependent changes result in significant changes in the A1-mode frequency at 187 cm-1, the line width of the E1-mode at 277 cm-1, and the normalized intensities of the E1-mode at 277 cm-1 and the B2-mode at 199 cm-1. It is shown that the intensity increase in Raman modes, with the [Ga]-content increasing in the range 0.9 < [Cu]/[Ga] < 1, is correlated to an increase in defect concentration and lowering of film crystallinity. Moreover, it is shown that the [Cu]/[Ga] fraction of Ga-rich films, used in solar cell device applications, can be calibrated with respect to the band width of the E1-mode