科研之友
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摘要
Tin oxide (SnO2) thin films, doped with different concentrations of bismuth (Bi), are prepared by the magnetron reactive sputtering technique. Microstructural, spectroscopic and electric transport measurements are performed and the results have been correlated. The crystallite size, which is evaluated from power X-ray diffraction (XRD) studies is in the 10-20 nm range. Bi is doped into SnO2 lattice as +5 valence state, leading to n type conductivity. The doped samples show the deterioration of the crystallinity with increase in Bi doping concentration, evidenced by the smaller crystallites and rougher surface compared with undoped ones. Due to highly disordered defects in the Bi-doped SnO2 films, the first order Raman-active mode inherent to SnO2 lattice shifts to lower wavenumber with the increasing of the Bi concentration. Based on Hall effect measurements, it is found that the sheet resistance dramatically increases up to 3.2 x 104 X/h with Bi doping level of 2 at.%, accompanied by a sharp decrease of the electron mobility mu. The temperature dependence of the resistance presents different functional relationship relying on the doping concentration, and a possible crossover of the carrier transport mechanism from 2D to 3D behavior is established when discussed in the framework of the weak localization and electron-electron interactions.
