Influence of the Potassium Chloride Concentration on the Physical Properties of Electrodeposited ZnO Nanowire Arrays

The structural, electrical, and optical properties of zinc oxide nanowire arrays electrodeposited from the reduction of molecular oxygen in aqueous solutions containing zinc chloride and potassium chloride are studied as a function of the potassium chloride concentration. The concentration is varied in a wide range (from 5 x 10(-5) to 3.4 M). The evolution of the lattice parameters suggests the formation of zinc interstitials, especially for [KCl] > 1 M. The donor density of the as deposited nanowires, which was determined from electrochemical impedance spectroscopy (EIS), varies between 7 x 10(18) and 4 x 10(20) cm(-3). Annealing in air (1 h at 450 degrees C) decreases the donor density to 10(17)-10(18) cm(-3), weakening the dependence on KCl concentration. The line width of the near-band-edge photoluminescence shows a correlation with the donor density. By correlating the variation of the lattice parameters, the donor density and the line width of the photoluminescence, we conclude that intrinsic defects play a dominant role. The incorporation of chlorine impurities appears to be of minor importance, but the concentration of chloride ions in the solution influences the formation of intrinsic defects by modifying the local composition of the electrolyte around the nanowires.