OPTICAL AND ELECTRICAL-PROPERTIES OF RADIO-FREQUENCY SPUTTERED TIN OXIDE-FILMS DOPED WITH OXYGEN VACANCIES, F, SB, OR MO

Tin oxide films doped with oxygen vacancies, F, Sb, or Mo were made by reactive rf magnetron sputtering of Sn, Sn-Sb, or Sn-Mo in Ar+O-2(+CF 4) onto glass heated to a temperature up to 530 degrees C. Electrical de resistivity, mobility, free-electron density, spectral optical prop erties, and microstructure were investigated as a function of sputteri ng parameters. Optimized deposition parameters gave SnOx(Sb,F) films w ith high luminous transmittance, low luminous absorptance, high infrar ed reflectance, and de resistivity down to 9.1X10(-4) Omega cm. Refrac tive index n and extinction coefficient k were evaluated from spectrop hotometric transmittance. In the luminous range, the films had 1.90<n< 2.0 and k of the order of 10(-2). Hall-effect measurements showed n-ty pe conduction with electron densities in the 10(20)-10(21) Cm-3 range. Band-gap broadening from 4.06 to 4.45 eV was observed with increasing electron density. X-ray diffractometry and transmission electron micr oscopy showed that the structure factor of the films depended on the o xygen content as well as on the specific doping species. A preferred d irection of film growth was probably also present. Transmission electr on microscopy indicated different grain sizes, between 6 and 30 nm, de pending on oxygen content, substrate temperature, and doping species. Optical and electrical properties were compared with results from a qu antitative model for wide band-gap semiconductors. The theory is based on heavy n doping by oxygen vacancies or by Sb or/and F and encompass es ionized impurity scattering of the free electrons. It was found tha t ionized impurity scattering, as well as an additional scattering mec hanism tentatively ascribed to grain boundaries, prevailed in the film s.