Highly (002) textured, ultra-thin (100–160nm), nano-crystalline zinc oxide thin films were grown by metal organic chemical vapour deposition. These films were characterized in terms of structure, microstructure, optical and carbon monoxide gas sensing characteristics. The room-temperature photoluminescence (PL) spectra of these films were characterized by two peaks: the first one at 387nm was due to the near band edge UV emission and the other one at about 496nm was green emission from defect levels. The PL intensity ratio of the defect level and near band edge emission (IDL/INBE) was argued to be an indicator of oxygen vacancy concentration of these films. The response (%) of carbon monoxide gas sensing was found to increase with the film thickness and maximized in film which was about 130nm thick. With further increase of film thickness the response % was found to be reduced. Good correlation was observed between the variation of the PL intensity ratio (IDL/INBE) and response% as a function of film thickness. It was argued that the concentration of oxygen vacancies in turn controls the gas sensing characteristics of the synthesized films. Finally, the interrelationship between oxygen vacancy concentration, film microstructure and gas-sensing characteristics of synthesized films was elucidated.

Role of Oxygen Vacancy in Optical and Gas Sensing Characteristics of ZnO Thin Films. S.Pati, S.B.Majumder, P.Banerji: Journal of Alloys and Compounds, 2012, 541, 376-9