Investigation of the growth process and optical transitions as a function of Ga content in CuIn1−xGaxSe2 thin films at 570 °C

The CuIn_1-xGa_xSe₂ (CIGS) growth process, as well as the fundamental optical transitions, at the growth temperature of 570 °C have been studied for various x = Ga/(In+Ga) ratios. Data acquired by spectroscopic ellipsometry in real time (RTSE) were used to extract this information which was then correlated with ex situ techniques such as AFM, SEM etc. The roughness extracted from RTSE indicates that the Ga content does not have a significant effect on this parameter, while all layers follow the Volmer-Weber growth process. The complex dielectric functions, (ϵ₁ ϵ₂), of CIGS at 570 °C as a function of x = Ga/(In+Ga) were also extracted from these RTSE data. By fitting critical point oscillators in the second derivative of ϵ₂, the dependence of the band gap on x and a bowing parameter were extracted for high measurement temperatures.