The Role of Spatial Potential Fluctuations in the Shape of the PL Bands of Multinary Semiconductor Compounds

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Abstract
Photoluminescence (PL) measurements of CuIn1-xGaxSe2 (x = 0.5) single crystals grown by the vertical Bridgmann technique were made at temperatures ranging from 11 K to 200 K and with various excitation powers. At low temperatures only one asymmetric PL band (BT-band) is present at 1.23 eV. It has a steeper decline on the high-energy side and nearly temperature independent low-energy side. At higher temperatures (T > 140 K) the BB-band becomes visible at 1.31 eV. We used an asymmetric double sigmoidal function to fit the experimental PL spectra. The results of this fitting can be interpreted to show the presence of spatial potential fluctuations in our samples. Observed dependencies would seem to reveal that the BT band is indeed connected with the recombination of a free electron with a localized hole. It is shown that these relatively deep localized states are probably formed due to potential fluctuations in highly compensated material and are not connected with any particular acceptor defect. We show that this model conforms to most of the discovered dependencies.

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