Nature of the AX center participating persistent photoconductivity effect in As-doped p-ZnO

Abstract

The possible nature of metastable capture centers giving rise to persist photoconductivity (PPC) effect in As-doped p-ZnO was investigated using the photoluminescence result. Through the plot of log σph vs. 1/T and temperature-dependent PPC-decay process, the metastable trapping centers were extracted to be 15.1, 178.2, 180.6, and 291.9 meV. The shallow level of 15.1 meV was related to the binding energy of the neutral acceptor bound exciton. Also, the deep levels of 178.2 and 180.6 meV were caused by complex acceptor states of AsZn-2VZn located at 185 meV above the edge of the valence band. Furthermore, the trapping center of 291.9 meV was corresponded to the hole capture barrier of VZn located at 300 meV above the valence band. Therefore, these trapping centers were deeply related to the AX centers originating the native defects due to VZn or defect complexes of the As-implanted dopant in ZnO. Also, these defects, induced by the metastable AX centers, were concluded to be responsible for the PPC effect.