Deep levels in the MBE ZnO:As/n-GaN diodes – Photoluminescence, electrical properties and deep level transient spectroscopy

Abstract

In this paper the current understanding of defects in acceptor doped ZnO is briefly reviewed. The results of investigations of ZnO:As/n-GaN heterojunctions which have been successfully fabricated by plasma assisted molecular beam epitaxy method are presented. The electrical properties of the junctions, as well as deep levels, have been studied by means of current-voltage (I-V), capacitance-voltage (C-V) characteristics and deep level transient spectroscopy (DLTS). Electrical measurements were supplemented by photoluminescence- (PL) along with secondary ion mass spectrometry (SIMS) and X-ray photoemission spectroscopy (XPS) investigations. The I-V measurements allowed for detailed analysis of current mechanisms, through which the presence of trap states in the investigated junction was confirmed. The C-V results proved that the depletion region of the diode is located within the ZnO:As layer. The DLTS measurements revealed the presence of three hole trap related signals. The activation energies and capture cross sections of these traps were determined and their possible origin has been ascribed. Obtained results allowed for better identification of defects found in the case of the analyzed heterostructure, as well as the studies of its electronic properties.