Effect of Co doping on structural, morphological and LPG sensing properties of nanocrystalline ZnO thin films

• Co doping along with Pd sensitization shows improvement in the sensor response.
• Effect of Co doping on structural and morphological properties is investigated.
• XPS studies show presence of Co in different chemical states at higher doping concentration.

Nanocrystalline cobalt doped zinc oxide (CZO) thin films were deposited on to the corning glass substrates by spray pyrolysis technique using zinc acetate and cobaltous nitrate as precursors. Structural, morphological, photoluminescence and gas sensing properties of the films with various Co doping concentrations were investigated. XRD patterns confirm that, films are polycrystalline with hexagonal (wurtzite) crystal structure. XPS reveals films are sub-stoichiometric in nature with Co present in two chemical states. SEM images show the films are compact, densely packed with hexagonal flakes and spherical grains on the surface. The direct band-gap energy increases from 3.27 to 3.33 eV with cobalt doping concentration. LPG response of the film increased with Co concentration up to 2 at% and decreased thereafter. Pd sensitized 2 at% CZO thin film shows 47% gas response as compared with 33% for un-sensitized CZO thin film. Film shows stable gas response even for 20 min in presence of LPG.