Investigations of lateral and vertical compositional gradients in Cu(In,Ga)Se2 prepared through Rapid Thermal Processing by highly spatially and spectrally resolved cathodoluminescence spectroscopy

We analyze Cu(In,Ga)Se2 thin films using highly spatially and spectrally resolved cathodoluminescence (CL) spectroscopy at low temperature (T=5 K). The films were deposited by means of a rapid thermal selenization process with growth times varying from 70 to 150 seconds. We find that lateral integral spectra exhibit a broad dominant peak with energies from 0.95 eV to 0.99 eV and a shoulder on the low-energy side. By varying the excitation density, a shift to higher energies of the main peak by 12.8 meV/decade can be observed for the samples with growth times of 100 s and 120 s. Investigations of the cross-sections reveal two distinct regions in the layer sequence. A Ga-rich layer next to the back contact can be identified showing lower luminescence intensities. In contrast, the layer on top reveals an In-rich concentration.