Hydrogen gas sensing properties of Pd/ZnO thin films grown on n-Si<100> substrates at room-temperature by thermal evaporation and sol-gel techniques: A comparative study

Abstract

The present paper compares the room temperature hydrogen (H₂) gas sensing properties of two Pd/nanocrystalline-ZnO thin film based Schottky contacts grown on n-type silicon (100) substrates by thermal evaporation and sol-gel techniques. The structural, surface and optical properties of the ZnO thin films under consideration are also presented. The Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) measurements have been carried out to study the surface morphologies and elementary compositions of the ZnO films,respectively. The X-ray diffraction (XRD) analysis shows that the ZnO thin films grown by both the methods are polycrystalline in nature with a hexagonal wurtzite structure. The optical band gaps of the films are estimated from the photoluminescence (PL) spectroscopy as 3.26 eV and 3.28 eV for thermal evaporation and sol-gel techniques, respectively. The current–voltage (I-V) measurements have been carried out to study the electrical and hydrogen (H₂) sensing characteristics of Pd/ZnO Schottky contacts fabricated on the ZnO thin films grown by the two methods under consideration. Both the Pd/ZnO contacts under consideration are observed to have a good Schottky behaviour under dark condition and a high response to H₂ gas with relatively short response and recovery times. Device fabricated by thermal evaporation shows better performance.