Optimized hydrogen sensing characteristic of Pd/ZnO nanoparticles based Schottky diode on glass substrate

The present work deals with the development of the Pd/ZnO naoparticles based sensor for detection of hydrogen (H-2) gas at relatively low temperature (75-110 degrees C). Pd/ZnO Schottky diode was fabricated by ZnO nanoparticles based thin film on glass substrate using sol-gel spin coating technique. These ZnO nanoparticles have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive x-ray spectroscope (EDS), and field emission scanning electron microscope (FE-SEM) which reveals the ZnO film having particles size in the range of similar to 25 to similar to 110 nm with similar to 52.73 nm surface roughness. Gas dependent diode parameters such as barrier height and ideality factor have been evaluated upon exposure of H2 gas concentration in the range from 200-2000 ppm over the temperature range from 75 to 110 degrees C. The sensitivity of the Pd/ZnO sensor has been studied in terms of change in diode forward current upon exposure to H-2 gas. Experimental result shows the optimized sensitivity similar to 246.22% for H-2 concentration of 2000 ppm at temperature 90 degrees C. The hydrogen sensing mechanism has been explained by surface and subsurface adsorption of H-2 molecules on Pd surface; subsequently, dissociation of H-2 molecules into H + H atoms and diffusion to trap sites (oxygen ions) available on ZnO surface, resulting in formation of dipole moments at Pd/ZnO interface. The variation in the sensitivity, response and recovery time with temperature of Pd/ZnO sensor has also been studied.