Effect of Cu/Ga ratio on deep-level defects in CuGaSe₂ thin films studied by photocapacitance measurements with two-wavelength excitation

The effect of the Cu/Ga ratio on properties of deep-level defects in CuGaSe₂ thin films were studied, using photocapacitance methods with two-wavelength excitation. The transient photocapacitance method, using a monochromatic probe light, determined two kinds of defects located at 0.8 eV and 1.5 eV above the valence band, respectively, the positions of which kept almost constant regardless of Cu/Ga ratio. In addition to the probe light, laser light with a wavelength of 1550 nm corresponding to 0.8 eV was then used to study the saturation effect of the deep-level defect at 0.8 eV above the valence band. The results suggest that the defect level at 0.8 eV acts as a recombination center at room temperature, and it becomes more effective in CuGaSe₂ films with a lower Cu/Ga ratio.