Trap‐sensitive relaxation of hot carriers in ZnO:Cu,Al

Abstract

Modulated photoconductivity measurements with x-ray excitation were performed on ZnO:Cu,Al thin films. We found a strong variation of the modulated photocurrent with temperature starting from the excitation energy approximately equal the binding energy of Cu 2p3 core electrons and above. Strong temperature sensitivity at ~280 K suggests participation of thermally activated trap states in the process of hot carrier relaxation. The shape of the temperature dependence was satisfactorily fitted by the respective calculation. No comparable deviations of the temperature sensitivity were observed when the Cu 2s electrons were excited. We explain the observations by assumption of fast local transitions from a valley in the conduction band into the trap state according to the symmetry selection rules.