Subgrain size inhomogeneities in the luminescence spectra of thin film chalcopyrites

We report near-field photoluminescence (PL) spectra of Cu(InGa)Se-2 thin films recorded with a lateral optical resolution of approximate to 200 nm and simultaneous detection of the sample topography. Our results reveal significant local variations in the PL spectra, specifically the PL yield, on length scales of 0.2-1.5 mu m. Local variations in both the splitting of quasi-Fermi levels mu and the band gap energy are quantitatively extracted from the PL spectra by applying Planck's generalized law. We show pronounced fluctuations of mu and the band gap on length scales below the grain size. These fluctuations are only weakly correlated with the topographic film structure. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3475018]