Investigation of deep-level defects in Cu(In,Ga)Se₂ thin films by two-wavelength excitation photo-capacitance spectroscopy

The properties of the defect level located 0.8 eV above the valence band in Cu(In_1-x,Ga_x)Se₂ thin films were investigated by a photo-capacitance method using a monochromatic probe light with an energy of 0.7 to 1.8 eV. In addition to the probe light, laser light with a wavelength of 1.55 μm, corresponding to 0.8 eV, was also used to study the saturation effect of the defect level at 0.8 eV. A suppression of electron-hole recombination due to saturation of the defect level was observed at room temperature while no saturation effect was observed at 140 K. The results suggest that the defect level at 0.8 eV acts as a recombination center at least at room temperature.