Photoluminescence studies of undoped and nitrogen-doped ZnO layers grown by plasma-assisted epitaxy

Nitrogen-doped ZnO layers grown on C-sapphire at 400degreesC by plasma-assisted epitaxy in oxygen and nitrogen mixed gas plasma were studied by photoluminescence measurements comparing to undoped ZnO layers grown in pure oxygen plasma. A new luminescence was observed around 3.27 eV with phonon-replicas at 20 K and we concluded that they are due to shallow donor-acceptor pair emission by excitation power dependence of the peak energy. The donor and acceptor levels were assigned as shallow levels located at 40meV below conduction bandedge and 135meV above valence bandedge, respectively. It was also indicated that Zn-rich condition should be given for efficient nitrogen-acceptor doping. (C) 2003 Elsevier B.V. All rights reserved.