Density of states in CuIn(SSe)2 thin films from modulated photocurrent measurements

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Abstract
Results of modulated photocurrent measurements in the temperature range between 180 and 300 K on polycrystalline CuIn(S,Se)2 thin films are presented. Modeling of the obtained phase shifts implies a continuous energetic distribution of traps in the band gap. A superposition of an exponential energetic distribution of traps with a characteristic energy of 60 meV and a Gaussian peak with a depth of 250 meV can explain the obtained phase shift and amplitudes between 250 and 300 K. For lower temperatures a change of the transport path, reducing the effective depth of the peak in the density of states and reducing the ‘‘attempt to escape frequency’’ is likely. At low temperatures the phase shift depends on the photon flux due to the separation of the demarcation levels whereas in the case of the higher temperatures no significant dependence on the light intensity could be detected.