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STRUCTURAL AND ELECTRICAL PROPERTIES OF UNDOPED SnO2 FILMS DEVELOPED BY A LOW COST CVD TECHNIQUE WITH TWO DIFFERENT METHODS: COMPARATIVE STUDY

N. D. Papadopoulos1, P. E. Tsakiridis1, E. Hristoforou1,*

Affiliation

  1. Laboratory of Physical Metallurgy, School of Mining and Metallurgical Engineering National Technical University of Athens 9, Iroon Polytechniou Street, 157 80 Zografou, Athens, Greece

Abstract

Uniform, conductive SnO2 thin films have been developed by a low – cost CVD technique using a simple, home-made setup. Two methods with different sources of oxygen were applied. The thin layers were deposited on glass substrates. Stannic chloride was used as the precursor and the substrate temperature varied from 485 to 545 oC. The microstructure and the surface morphology of the produced films were examined by X-Ray Diffraction and scanning electron microscopy, with EDAX analysis. The films were found to be polycrystalline, presenting a preferred orientation along the (110) plane. Thickness of films varied from 150 nm to 400 nm. Extended study of the mechanism of diffusion of sodium ions out of the glass as well as its effects on film’s quality was carried. Crystals of NaCl formed on the matrix of films, which had been grown with air functioning as the oxidizer. Measurements of the mean surface’s roughness were conducted by a profilometer. When pure oxygen was used, the produced films presented a smoother surface without any pinholes or undesirable crystal formation. Electrical resistivity at room temperature and in the range from 25 to 250 oC was also measured. Films of high conductivity were obtained for both methods at deposition temperatures between 515 and 545 oC. For films of high crystallinity grain scattering and scattering from ionised impurities are the major factors influencing conductivity. When air is used as the oxidizer, films develop fully at higher deposition temperatures. In this case however, oxidation diminishes vacancies, which are present at a high degree since the oxygen concentration in air is low. In both methods, annealing in air improved the film crystallinity and conductivity..

Keywords

CVD, Thin films, Tin oxide, Oxidizer, Characterization.

Submitted at: June 28, 2005
Accepted at: Sept. 22, 2005

Citation

N. D. Papadopoulos, P. E. Tsakiridis, E. Hristoforou, STRUCTURAL AND ELECTRICAL PROPERTIES OF UNDOPED SnO2 FILMS DEVELOPED BY A LOW COST CVD TECHNIQUE WITH TWO DIFFERENT METHODS: COMPARATIVE STUDY, Journal of Optoelectronics and Advanced Materials Vol. 7, Iss. 5, pp. 2693-2706 (2005)