Structural and Optical Properties of Electrochemically Grown Fluorine Doped Zinc Oxide Rods

Abstract

In this study, undoped and fluorine (F) doped zinc oxide (ZnO) rods were electrochemically deposited on p-type Si substrates in an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)(2)center dot 6H(2)) and hexamethylenetetramine (C6H12N4) by using chronoamperometry method. Different atomic ratios (1-35%) of ammonium fluoride (NH4F) were used as a dopant salt. Electrochemical depositions were performed by applying a constant potentiostatic voltage of -1.0 V for 90 min at 90 degrees C bath temperature. The effects of F doping on the structural, morphological and optical properties of ZnO rods were investigated by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence (PL) techniques. The crystal structure and orientation of the rods were investigated by XRD patterns and all rods were found to have hexagonal wurtzite structure. SEM results stated that all of the obtained rods are consist of hexagonal ZnO rods with varied lengths and dimensions. Besides, SEM micrographs reveal that as the doping amount increased, rods became thicker and poor surface coverage observed. PL measurements reveal that undoped ZnO rods exhibit a PL emission peak at 372 nm, a weak broad green-yellow emission centered at 560 nm and a weak red emission at 738 nm. The strong ultraviolet (UV) emission can be attributed to near band edge emission whereas the bands at higher wavelength side can be attributed to oxygen vacancies. It was observed for F-doped ZnO rods that the UV emission peak showed a blue shift with respect to the undoped one. In addition, it was demonstrated that the green-yellow band PL emission intensities increased up to a doping level of 5% and decreased with further increase in the doping level.