Microstructural properties and carrier transport mechanism in Bi-doped nanocrystalline SnO 2 thin films

摘要

Tin oxide (SnO 2 ) 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 10–20nm range. Bi is doped into SnO 2 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 SnO 2 films, the first order Raman-active mode inherent to SnO 2 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 3.2×10 4 Ω/□ with Bi doping level of 2at.%, accompanied by a sharp decrease of the electron mobility μ . 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.