MOCVD grown ZnO thin film gas sensors: Influence of microstructure

• Textured ZnO ultra thin films are grown using MOCVD technique.
• Growth mode dependent microstructures are fabricated.
• The microstructure formation is understood on the basis of van der Drift model.
• Hall effect measurement provides reliable results.
• Correlation between the microstructures and the gas sensing behavior is explained.

The present work is aimed to investigate the influence of microstructure on the gas sensing characteristics of ZnO thin films. By controlling the deposition parameters we have successfully grown ZnO thin films of different microstructures on quartz substrates by MOCVD growth technique using diethyl zinc and tert-butanol as zinc and oxygen precursors, respectively. X-ray diffraction pattern shows that the films are textured along (0 0 2) plane. FESEM images reveal the uniform deposition of fine grains with varying microstructures. Growth mode dependent microstructure formation is explained on the basis of a simple model. The optical characterization reveals that the films are transparent in the visible range with band gap energy in the range 3.234–3.217 eV. The effect of microstructure on the electrical parameters of the ZnO such as carrier concentration, resistivity and Hall mobility is understood through Hall effect measurement using standard Van der Pauw geometry. The gas sensing characteristics of the grown films is investigated as a function of temperature and gas concentration in CO test gas environment. The observed results are analyzed on the basis of the variation of microstructures of the grown films.