UV Photoconductivity of Nanocrystalline TiO_2 Films Annealed in Oxygen
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概要
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The effects of annealing in reactive gases (H_2, N2, O_2) upon the optoelectric properties of nanophased titanium dioxide (TiC_2) prepared by chemical vapour deposition (CVD) were investigated. The nanocrystalline structure containing nanosize grains and pores was analyzed by grazing-incidence small-angle scattering of synchrotron radiation (GISAX). The annealing (up to 1073 K) in H_2 and N_2 generally proved detrimental to photoconductivity due to the overall increase of the electrical conductivity of the samples. In this work, the result of UV (248-404 nm) photoconductivity measurements on TiC_2 films annealed in O_2 at 773 K and 1073 K are presented. A rather long illumination time (typically 2 h) enabled us to clearly distinguish two types of nonequilibrium photoconductivity variations with time. A fast exponential photoconductivity increase occurred during the initial stage of irradiation, while a slow power-type increase was observed in the later stage. A nonlinear combination of both functions was used in a numerical fitting procedure, which allowed precise determination of the asymptotic value of exponential photoconductivity increase. A relative quantum efficiency for both as-prepared and annealed samples exhibits a nonmonotonic variation with photon energy. Such wavelength-dependence variation might be due to the electronic density function structure at the valence-band edge, or near-valence-band levels in the gap. Generally, the samples annealed at higher temperatures exhibit a higher quantum efficiency and shorter time constants of the excitation processes, in the examined UV range.
- 社団法人応用物理学会の論文
- 2002-09-15
著者
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Radic Nikola
Rudjer Boskovic Institute, Division of Materials Science
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Car Tihomir
Rudjer Boskovic Institute, Division of Materials Science
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Turkovic Aleksandra
Rudjer Boskovic Institute, Division of Materials Science