Thickness Dependence of Transport Properties of Doped Polycrystalline Tin Oxide Films

Tin oxide films were deposited by chemical vapor deposition on borosilicate and fused silica substrates using dibutyltin diacetate (DBTD) as tin feedstock and or as dopants. The film growth rate was measured as a function of dopant/DBTD ratio, temperature, and film thickness. Scanning electron microscopy and x‐ray diffraction spectra of the films were used to determine the grain sizes and the preferential orientations of the crystallites in the film as a function of film thickness. Optical and electrical properties were measured. A model is proposed to elucidate the variation of transport properties of doped as a function of film thickness. It could be shown with this model that the thickness dependence of the conductivity of doped and films could be analyzed in terms of carrier concentration taking into consideration deep‐level compensation. The number of carriers is decreased by electron trapping at Sb(III) or Sn(II) surface states when antimony or fluorine are used as dopant, respectively. The model based on results of the literature related to a single crystal with (110) orientation is extended in this work to other crystallite orientations. The present analysis indicates that deep levels appear only on the grain boundary surfaces with (110), (211), and (301) orientations, and not on the (200) and (400) ones. The concentration of free carriers can be calculated on the basis of x‐ray diffraction spectra indicating an estimate of the relative fraction of the crystallites with each orientation as a function of the film thickness. The conductivities of the films can be computed using this model and taking a single value for the electron mobility of 19 cm² (V‐s)⁻¹ for all film thicknesses and a total donor concentration of . All the obtained experimental data can be accounted for exclusively on the basis of film‐thickness‐dependent carrier concentration.