Tailoring the electronic and elastic properties by varying the composition of the CuGa_1-xAl_xS2 chalcopyrite semiconductor

The influence of composition and external hydrostatic pressure on the structural, electronic and optical properties of the CuGa_1-xAl _xS2 (x = 0, 0.25, 0.5, 0.75, 1.0) chalcopyrite semiconductor was analysed by means of the first-principles calculations. Dielectric functions and optical absorption spectra were calculated for all considered aluminum concentrations. The pressure coefficients of the calculated band gaps and the position of the lowest in energy absorption peaks were extracted from the calculated data. One of the main results is that substitution of 25% of gallium by aluminum (thus forming the CuGa₀.75Al ₀.25S₂ semiconductor) increases absorption in the visible part of the solar spectrum by about 6%, which can be important for solar cell applications.