Stable p-Type Doping of ZnO Film in Aqueous Solution at Low Temperatures

Zinc oxide (ZnO) is a wide band-gap material with excellent optical properties for optoelectronics applications. However, device fabrication has been hampered by difficulties in obtaining a stable p-type doping. Here, we present the first report on the growth and doping of ZnO film through the incorporation of potassium (K) from group I in aqueous solution at 90 °C to yield a stable p-type doping. The contribution of potassium toward p-type conductivity is confirmed using Hall effect measurements and SIMS. A new growth strategy was introduced to obtain a good film coverage with a lower native defect density without the use of surfactants. Photoluminescence measurements confirmed the reduction of defect-related emissions and enhancement of UV band-edge emissions. Variation of carrier concentrations with temperature points to the presence of unstable hydrogen donors that can be removed by annealing at temperatures above 400 °C for extended durations. The instability of these hydrogen defects is attributed to the low growth temperatures. Finally, a p-ZnO/n-GaN junction is demonstrated to have a rectifying I−V characteristic and two dominant electroluminescence peaks in the UV range of 370−390 nm, as well as a broad yellow-orange peak.