The effect of boron on the doping efficiency of nitrogen in ZnO

Stable p-type boron-nitrogen codoped ZnO thin films were prepared by plasma-assisted molecular beam epitaxy. The incorporations of boron and nitrogen into ZnO, identified by X-ray diffraction and X-ray photoelectron spectroscopy, led to improvement in p-type conductivity of ZnO with respect to nitrogen monodoped ZnO. It was ascribed to the marked enhancement of nitrogen doping efficiency due to the existence of two types of chemical states of nitrogen atoms: the nitrogen substituting at oxygen site with nearest neighbor of Zinc atom (NO-Zn bonding), and the nitrogen locating at the nearest neighbor of boron atom (NO-B bonding). The strong interaction between the boron and nitrogen makes the complex of BZn-nNO (n = 3 or 4) be a shallow acceptor, which is responsible for the observed p-type behavior.