Determination of defect distributions from admittance measurements and application to Cu(In,Ga)Se-2 based heterojunctions

A method to deduce energy distributions of defects in the band gap of a semiconductor by measuring the complex admittance of a junction is proposed. It consists of calculating the derivative of the junction capacitance with respect to the angular frequency of the ac signal corrected by a factor taking into account the band bending and the drop of the ac signal over the space charge region of the junction. Numerical modeling demonstrates that defect distributions in energy can be reconstructed by this method with high accuracy. Defect distributions of polycrystalline Cu(In,Ga)Se-2 thin films are determined by this method from temperature dependent admittance measurements on heterojunctions of Cu(In,Ga)Se-2 with ZnO that are used as efficient thin film solar cells. (C) 1996 American Institute of Physics.