Charge carrier transport in polycrystalline CuGaSe2 thin films

The mechanism of charge carrier transport in stoichiometric polycrystalline CuGaSe₂ has been studied in the temperature range of 80-350 K using Hall effect and conductivity measurements. The layers were grown on soda-lime glass substrates by physical vapour deposition. At 300 K we found mobility values in the range of 10-20 cm²/Vs. A thermally activated behavior of the mobilities in these films was observed in the temperature range of 150-300 K. Intergrain potential barriers limiting the charge carrier transport were determined to vary between 60 and 130 meV. Using the grain boundary barrier trapping model developed for polycrystalline Si the density of charged states at the grain boundaries was calculated to be about 1.2e12 cm^-2. This value does not depend on the net doping concentration of the samples significantly, suggesting that the position of the relevant defect states at the grain boundaries is above the Fermi level. Above 300 K the carrier transport is limited not only by potential barriers but also the in-grain mobility.