Photoacoustic spectroscopy of sprayed CuGa_xIn_1-xSe₂ thin films

CuGa_xIn_1-xSe₂ thin films have been produced using spray-pyrolysis. The layers were deposited onto Mo-coated soda-lime glass at a substrate temperature of 623 K, and the gallium content of the layers varied. The layers were investigated using photoacoustic spectroscopy. The normalised photoacoustic spectra of CuGa_xIn_1-xSe₂ films with x = 0, 0.2, 0.4 and 0.5 showed a sudden fall in the photoacoustic signal at photon energies of 0.99, 1.15, 1.27 and 1.36 eV, respectively, which correspond to the respective direct energy band gaps of these films. The photoacoustic spectra also showed peaks at 0.75, 0.78, 0.82, 0.86 and 0.88 eV, respectively, in the sub-band gap region, which have been attributed to the defect states within these films.