Electrical Transport Properties Of F Doped SnO₂Films

F doped tin oxide （FTO） film is a promising material with applications in solarcells, flat panel displays and many other areas due to its high transparency in visiblerange and excellent conductivity. A large amount of works have been devoted to thestudy of FTO films, over the years, both in theorey and experiment. Current works onthe origins of the combined properties of high electrical conductivity and high opticaltransparency of FTO are mainly based on ab initio band-structure calculations.According to the calculation results, FTO exhibits free-electron-like characteristic.Meanwhile, a majority of studies in experiment focused on the deposition techniques,aiming to obtain high quality FTO films, systematical experimental works to revealthe electrical transport mechanisms in FTO films are very limited. In addition,material performance largely depends on its structure. Treatment will change thestructure and morphology, and then change the performances of the films.We have systematically investigated the electrical transport process of FTO films.We found that the temperature dependence of the resistivities of the FTO films can bewell described by the Bloch-Grüneisen law from300K down50K, while the carrierconcentrations are almost invariable. These results demonstrate that FTO filmspossess metallic transport nature. Only the diffusive thermopowers which varieslinearly with temperature from300to10K can be observed. The phonon-dragthermopowers is completely suppressed due to the long electron-phonon scatteringtime in the compound. Through the analysis of resistivity and thermopower, we foundthat FTO films possess the free-electron-like behavior, and obey the Boltzmanntransport equation. Whereas below50K, the resistivities slightly increasing with thedecrease of temperature originate from the quantum effects （weak localization andelectron-electron interaction effects）. According to the weak-localization theory, wehave the relationship between the electron dephasing rate and temperature. At lowtemperature, the electron-electron scattering process dominated the dephasing from.Our observation quantitatively demonstrates the validity of the electron-electronscattering theory in three-dimensional （3D） disordered conductors. Carrierconcentrations are very high in general3D disordered metals, which makes theelectron-phonon scattering rate larger than the electron-electron scattering rate. Butthe carrier concentrations in our films are~3orders of magnitude lower than those in metals, which resulted in a greatly raised electron-electron scattering rate and leavedthe electron-electron scattering rate dominating the dephasing from. Therefore, itprovided us with the chance to test the theory of electron-electron scattering theory in3D disordered conductors.Through the study of heat treatment which influences the film properties of thetransparent conductive oxide, we found that FTO films have excellent thermalstability, also heat treatment can effectively improve its structure and enhance theoptical and electrical properties. Compared with FTO films, AZO films have poorthermal stability noticeably, annealing severely damaged its optical and electricalproperties.