Unfolding the conductivity reversal n- to p-type in phosphorus-doped ZnO thin films by spin-on dopant (SOD) process

Abstract

Phosphorus doping induced p-type doping in ZnO thin films based on spin-on dopant (SOD) process is reported in this article. Owing to the reduced dependence on the conventional amenities for diffusion/ion-implantation doping, the SOD process provides a simple and cheap doping method. The effect of SOD process temperature on conductivity ZnO thin films is investigated by altering the temperature from 700°C to 1000°C. Systematic field emission scanning electron microscopy analysis demonstrates the impact of doping temperature on the morphological properties of SOD. The x-ray diffraction measurements reveal that the p-type ZnO thin films had (002) preferred crystal orientation. At the same time, x-ray photoelectron spectroscopy validated the formation of the PZn–2VZn complex, which was responsible for the acceptor behaviour of films. Moreover, the photoluminescence spectra tracked down that the origin of 3.35 and 3.31 eV emission peaks is due to the acceptor bound exciton and free-electron to acceptor level transitions, respectively. Finally, an elevated hole concentration of 2.09 × 1016 cm−3 is achieved with a resistivity of 1.14 Ω-cm at 800°C doping temperature. However, the film doped at 900°C and 1000°C showed n-type behaviour due to the generation of high concentration donor defects. Here, we successfully demonstrate that the SOD process has great potential to produce high-quality p-type ZnO thin films suitable for optoelectronic devices applications.