Piezoelectric photothermal investigation of proton irradiation induced defects in CuInSe2 epitaxial films

Proton irradiation damage for CuInSe2 (CIS) solar cell material was investigated by using a piezoelectric photothermal spectroscopy (PPTS) from the viewpoint of nonradiative transition. Stoichiometric and Cu-rich thin film samples were grown on GaAs substrate for the measurements. Among the observed peaks at 1.01, 0.93 and 0.84 eV for the proton irradiated samples at room temperature, two peaks at 1.01 and 0.93 eV were attributed to the free exciton and the intrinsic defect level transitions, respectively. Since the peak at 0.84 eV could not be observed for the sample before irradiation, we considered that this peak was induced by the proton irradiation. Our results indicated that the irradiation-induced Se vacancy played an important role for PPT signal generation. The recovery for the irradiation damage was also observed by this technique. Therefore, we concluded that the PPTS technique was a powerful tool for studying the defect level in the irradiated semiconductor thin films.