Effect of NaZn/Nai ratio on structural, optical, and electrical properties of Na-doped ZnO thin films

Abstract

In this paper, Na-doped ZnO (NZO) thin films were prepared via a dip-coating sol-gel method with Na doping content in a range of 0 at. %–3 at. %. X-ray photoelectron spectroscopy analysis showed that the NaZn/Nai ratio (r) increased with Na doping contents from 1 at. %–3 at. %. The effect of the NaZn/Nai ratio on the structural, optical, and electrical properties of NZO thin films was investigated. As the NaZn/Nai ratio increased, the lattice constant exhibited a continuous increase and resulted in the presence of increasing compressive stress in the NZO films. When the NaZn/Nai ratio was less than 1 (r<1), the electron concentration of NZO films increased continuously. However, when r>1, it decreased. The Hall mobility was mainly limited by ionized impurity scattering and displayed a decrease trend with the increasing NaZn/Nai ratio. Due to the Burstein-Moss effect, the optical energy band gaps (Eg) of NZO films got slightly enlarged as compared with that of the undoped ZnO film. Considering the relationship between the Burstein-Moss shift and the carrier concentration, the enlargement of Eg was actually determined by the NaZn/Nai ratio as well as the doping content.