Extrinsic Doping of Electrodeposited Zinc Oxide Films by Chlorine for Transparent Conductive Oxide Applications

A systematic study of n-type zinc oxide thin films electrodeposition in presence of chloride ions is presented in this article. The incorporation of chlorine during the growth is characterized by several techniques, and its influence on the optoelectronic properties of the films is explored. Different deposition conditions have been tested; depending on the support electrolyte nature (nitrate or perchlorate) and on the chlorine concentration introduced in the bath, a large range of carrier concentrations has been reached (from 7.4 x 10(17) cm(-3) for a nitrate electrolyte without chloride ions addition to 9 x 10(19) cm(-3) in perchlorate conditions with a chloride concentration of 0.1 M). This evolution of the doping concentration evaluated by Mott-Schottky measurements and confirmed by Raman spectroscopy has a great effect on the optical transmission of the films. The increase in the doping concentration tends to shift the absorption edge to higher energies and to induces the decrease of the transmission in the near-infrared range because of the free carrier absorption. We finally propose a model to explain the effective n-type doping of ZnO with Cl, based on the intrinsic and extrinsic defects of the system.