Optimization of Photosensitivity of Ultraviolet Sensors Based on ZnO Nanorods Etched with ZnO Nanopowders Using Taguchi Method

Abstract

In the present work, ZnO nanorods were synthesized on ZnO seed layer by a hydrothermal method and then etched in zinc nitrate solution, including ZnO nanopowder. To optimize the effective factors of etching solution such as zinc nitrate concentration, ZnO nanopowder concentration, and solution temperature, Taguchi experimental design with orthogonal matrix, L16, was used. Morphological and structural features of etched ZnO nanorods were analyzed by means of FESEM, AFM, and XRD. The morphological results showed that the etching process is accompanied by a decrease in length and diameter of ZnO nanorods about 23 nm and 480 nm, respectively. XRD patterns showed that the (002) peak intensity is significantly reduced by nanorod etching. The UV sensor devices were fabricated in metal-semiconductor-metal configuration based on etched ZnO nanorods and the effect of the etching factors on UV sensitivity was systematically studied. Etching in high solution concentration and high temperature led to increase the sensitivity in the range of 103-105. Under optimal conditions (zinc nitrate solution 0.01 M, ZnO nanopowder concentration 0.0225 g/L and temperature 70°C), a very high sensitivity to UV illumination was obtained (~ 1.1×105). Also, a direct relationship was observed between the decrease in diameter caused by etching and the increase in sensitivity of the UV sensors.