Room temperature deposition of stable p-type ZnO:N thin films through chemical species modulation using reactive pulsed laser deposition

Abstract

Low temperature processing as well as long-term electrical stability are required to match p-type ZnO thin films with flexible electronics applications. Herein, ZnO and ZnO:N thin films were deposited at room temperature by reactive pulsed laser deposition of a zinc metallic target. Several ZnO thin films were obtained by varying the oxygen working pressure from 1.2 × 10-5 Torr to 3.5 × 10-2 Torr. Chemical concentration was smoothly tuned as demonstrated by in situ X-ray Photoelectron Spectroscopy. Introducing and varying both N2 and O2 fluxes at a constant pressure, N-doped ZnO films from 0.3 at.% to 5 at.% were deposited. Adjusting the N2/O2 flux ratio, p-type ZnO:N films were successfully achieved, exhibiting a carrier concentration of 5.3 × 1018 cm−3, resistivity of 2 Ωcm, and mobility of 0.5 cm2V-1s−1. Four representative p-type samples were analyzed to confirm chemical and electrical reproducibility. Electrical properties of one of these films were measured again nine months after deposited, and p-type conductivity was still observed. Cathodoluminescence revealed green-dominant emissions in n-ZnO and UV-dominant emissions in p-ZnO:N films as nitrogen doping effect. Finally, a p-n diode was fabricated using photolithography, exhibiting rectification performance even nine months after deposited. P-type ZnO:N presented here are suitable for flexible electronics devices fabrication.