AVS 46th International Symposium
    Thin Films Division Wednesday Sessions
       Session TF-WeA

Paper TF-WeA7
Properties of Fluorine-Doped Tin-Oxide Films

Wednesday, October 27, 1999, 4:00 pm, Room 615

Session: Transparent Conductive Oxides
Presenter: X. Li, National Renewable Energy Laboratory
Authors: X. Li, National Renewable Energy Laboratory
S. Asher, National Renewable Energy Laboratory
R. Ribelin, National Renewable Energy Laboratory
P. Sheldon, National Renewable Energy Laboratory
T.A. Gessert, National Renewable Energy Laboratory
Correspondent: Click to Email
Conductive tin-oxide (SnO@sub 2@) films are used extensively for transparent electrodes in electrochromic devices, flat-panel displays, and thin-film photovoltaic solar cells. SnO@sub 2@ with a tetragonal structure is naturally an n-type semiconductor because of a deviation from stoichiometry. With n-type dopants such as antimony, chlorine, and fluorine (F), very high electrical conductivity can be obtained. In this study, we investigated F doped SnO@sub 2@ films produced by low-pressure metal organic chemical vapor deposition. Tetramethyltin (TMT), oxygen, and bromotrifluoromethane (CBrF @sub 3@) were chosen as precursors. Due to the high volatility of CBrF@sub 3@ precursor, the F doping efficiency is strongly dependent on the substrate temperature and reaction chamber pressure. Secondary ion mass spectrometry (SIMS) analysis has revealed that the F doping level depends logarithmically on the CBrF@sub 3@ partial pressure, and the electronic concentration depends logarithmically on the F doping level. SIMS results also show that the F doping level remains constant through the film thickness, and that F does not diffuse from a doped layer into an undoped layer. Hall measurements show the electron mobility (µ) of the film increases with the doping level, which contrary to what is expected from ionized impurity scattering. For undoped SnO@sub 2@ films, the µ is ~1 cm@super 2@/V-s and electron concentration is low-10@super 18@/cm@super 3@. For F doped SnO@sub 2@ films, the electron concentration increases to mid-10@super 20@/cm@super 3@, and µ increases to 40 cm@super 2@/V-s. The optical and structure properties of doped and undoped SnO@sub 2@ films were also compared. Spectrophotometry demonstrated that the fluorine-doped film had a higher absorption than the undoped film. X-ray diffraction texture analysis revealed that as F is added to the film, the film orientation changes from random to a strong preference toward the (200) direction.