Radiative recombination on ion-induced defects in thin films of Cu(In, Ga)Se$_{2}$ solid solutions

In thin films of Cu(In, Ga)Se$_{2}$ solid solutions radiation-induced effects after irradiation of hydrogen ions with an energy of 2.5, 5 and 10 keV with dose of $\sim$3$\times$10$^{15}$ cm$^{-2}$ were studied. A comparative analysis of the optical characteristics of non-implanted and implanted Cu(In, Ga)Se$_{2}$ thin films was carried out based on the measurements of photoluminescence spectra and the luminescence excitation spectra at liquid helium temperature of $\sim$ 4.2 K. The bandgap of Cu(In, Ga)Se$_{2}$ solid solutions determined from the data of mathematical processing of the luminescence excitation spectra was $\sim$ 1.171 eV. An intense band with a maximum of $\sim$ 1.089 eV was found in the photoluminescence spectra of non-implanted and hydrogen-implanted Cu(In, Ga)Se$_{2}$ thin films caused by the recombination of free electrons with holes localized in the tails of the valence band. It was established that appearance of intense broad bands in the photoluminescence spectra with maxima in the energy range of $\sim$ 0.92 eV and $\sim$ 0.77 eV is due to radiative recombination of nonequilibrium charge carriers at deep energy levels of acceptor type ion-induced defects formed in the bandgap of Cu(In, Ga)Se$_{2}$ solid solutions. The conditions for the appearance of the ionic passivation effect of dangling electronic bonds on the surface and in the bulk of Cu(In, Ga)Se$_{2}$ polycrystalline films, possible nature of point defects in the structure and the mechanisms of radiative recombination are discussed.