Zno Nanowires Electrodeposited for UV Detector Applications

Abstract

In the last years, wide band gap semiconductors have received great interest due to their wide application range. Specifically, one-dimensional structures of these semiconductors are candidates for many applications. ZnO is an ideal candidate, as it is an n-type semiconductor with a hexagonal structure, a direct wide band gap of 3.36 eV, high electron mobility, and large excitation energy of 60 meV at room temperature. This semiconductor exhibits an efficient emission in the ultraviolet and visible range, so it is also promising for UV detection applications. ZnO one-dimensional structures (nanowires) are a promising candidate for efficient UV detectors if they fulfill three requirements: high aspect ratio (length/pore diameter) to obtain high on/off current ratios in UV detectors, oriented along the c-axis of the hexagonal structure to reach high electrical properties for the photodetector, and ZnO nanowires should be ordered perpendicular to the substrate to provide excellent light trapping and improve absorption. In this study, ZnO nanowires have been grown at constant electrochemical deposition. Electrodeposition of ZnO was performed using a standard three-electrode cell, where the working electrode was home made anodic aluminum oxide (AAO) templates, the counter electrode was a Pt mesh, and the reference electrode was Ag/AgCl. The electrolyte used in the electrodeposition was peroxide solution (0.005 M ZnCl2 + 0.1 M KCl + 0.04 M H2O2). ZnCl2 concentration were changed from 0.001 M to 0.01 M. The electrodeposition temperature was 70, 75, and 80 °C. The morphology, uniform growth, and filling ratio were controlled by the ZnCl2 concentration, applied potential, and electrodeposition temperature. At 70 °C and using 0.005 M ZnCl2 in the electrolyte, high aspect ratio, uniform growth, and filling ratio ZnO nanowires were obtained by Scanning Electron Microscopy. The crystallographic structure of the nanowires was controlled by applied potential around the reduction potential of ZnO. X-Ray Diffraction confirms that the nanowires are pure ZnO. The main advantages of growing ZnO nanowires by electrodeposition into AAO are the order of the nanostructures, and perfect control nanowires geometry. Moreover, the electrical properties can be measured in ZnO nanowires embedded into AAO, after removing AAO, and single nanowires. The effect of the pore diameter and length of ZnO nanowires on IV curves, and photoresponse is a wide field waiting to be explored.