Defects and transport in the wide gap chalcopyrite CuGaSe2 Original Research Article

Composition dependent photoluminescence studies and electrical transport investigation on single and polycrystalline CuGaSe2 films are summarized: photoluminescence reveals two acceptors 60 and 100 meV deep, with the deeper one dominating for higher Cu-excess, and one donor, 12 meV deep. The lower energy emissions in Cu-poor material are not due to additional defects but due to fluctuating potentials. Temperature dependent mobility shows phonon scattering as the dominating scattering mechanism around room temperature and the transition to hopping conduction at lower temperatures for material grown under moderate to low Cu-excess. The transport in polycrystalline films is determined by grain boundary barriers around 100 meV high. The acceptor depth determined from temperature dependent charge carrier concentrations shows an infinite dilution limit of 150 meV. Increasing acceptor concentration leads to increased compensation, indicating self-compensation. The effect of Na appears to be the increase in acceptor concentration and thus increase in net doping, in spite of increased compensation.