Radiative recombination in CuInSe2 thin films

Abstract

We perform a detailed analysis of the radiative recombination processes in CuInSe 2 thin filmsgrown by multisource physical vapor deposition. The photoluminescence and photoluminescence excitation spectra are investigated as a function of stoichiometry, temperature and excitation intensity. Using samples with a large composition gradient, we are able to obtain a coherent picture of the optical transitions in the films. The broad–band photoluminescencespectrum typical for In–rich films breaks into a number of well–defined emission lines in Cu–rich CuInSe 2 . At low temperatures, emission peaks due to free–exciton, bound–exciton, and free–to–bound recombination are identified in Cu–rich films. The spectra of In–rich films tend to be dominated by donor–acceptor transitions. From the optical spectra, excitonionization energies and the temperature dependence of the band gap are determined. The observed optical transitions are related to intrinsic defects.