Fabrication and Characterization of ZnO/p-Si and TiO sub(2)/p-Si Heterojunctions for Hydrogen Detection-Influence of Pd Functionalization

Nanocrystallyne n-ZnO and p-TiO sub(2) thin films were deposited on crystalline Si substrate by the simple and low-cost sol-gel method. The surfaces of nanocrystalline ZnO and TiO sub(2) were modified by PdCl sub(2) solution to passivate the defect states and to improve the gas sensitivity. Both unmodified and Pd modified sensors with Pd-Ag/n-ZnO/p-Si/Al and Pd-Ag/p-TiO sub(2)/p-Si/Al device structures were exposed to different hydrogen concentrations (0.01%, 0.05%, 0.1%, 0.5%, and 1%) at the optimum biasing voltage and temperature. The effect of gas response was investigated using nitrogen as well as synthetic air as the carrier gas. Both the sensor configurations showed the improved gas response after surface treatment with Pd ions. Surface modified p-TiO sub(2) sensors recorded higher gas response (78%), response time (3 s), and recovery time (74 s) compared with ZnO sensors under the similar conditions.