Improved Hydrogen Sensing Characteristics of ZnO/p–Si Heterojunction by Functionalization of Sol–Gel Grown Nanocrystalline ZnO Films
Abstract:Nanocrystalline n-ZnO thin film was deposited on p-type silicon substrate (2–5 Ω cm resistivity and (100) orientation) by a simple and low cost sol–gel dip coating method. The surface of the deposited ZnO layer was chemically treated by PdCl2 solution. Two types of sensor structures (Pd–Ag/ZnO/p–Si/Al and Pd–Ag/Pd:ZnO/p–Si/Al) were fabricated and tested for hydrogen. The hydrogen response of the Pd treated ZnO surface was significantly enhanced (64% response and 83 sec response time) compared to the untreated ZnO surface (38% response and 156 sec response time). The long-term stability of the heterostructures was also improved after Pd treatment. Pd dispersion on ZnO surface reduces to a large extent the surface states associated with the polycrystalline ZnO thin film and enhances hydrogen chemisorptions by lowering the adsorption activation energy. The barrier height modulation at ZnO/p–Si junction via strong dipole formation at the Pd–Ag/ZnO interface on exposure to hydrogen improves the sensing characteristics.
Document Type: Research Article
Publication date: 2012-01-01
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