Chemical shifts and optical properties of tin oxide films grown by a reactive ion assisted deposition

Highly oriented nonstoichiometric tin oxide thin films were grown by a reactive ion assisted deposition onto Si(100) and glass substrates at room temperature as a function of relative ion (O)/atom (Sn metal) arrival ratio, and concurrently the deposited ion energy per atom (eV/atom) were changed from 10 to 100 eV/atom. As-deposited tin oxide films show preferred orientation along the SnO2〈101〉 axis and the x-ray diffraction peak intensity appears maximum at an average energy of about 50 eV/atom. From quantitative Auger electron spectroscopy, characteristic transitional Auger peaks of Sn metal MNN transitions were shifted to lower kinetic energies by 4–6±1.0 eV as the Sn4+ component becomes dominant in the deposited tin oxide films and the position of O KL1,2L2,3 transition line was also shifted to lower kinetic energy by 1–2±1.0 eV as the composition of deposited tin oxide films were changed from SnO to SnO2, respectively. On the basis of a tin 3d core level and O 1s spectra analysis by x-ray photoelectron spectroscopy, the sizable chemical shift of different valencies between stannous tin (Sn2+:SnO) and stannic tin (Sn4+:SnO2) was 1.0±0.02 eV and that of O 1s was 0.87±0.02 eV, and those values show larger shifts than previously reported ones. The refractive index n of as-deposited tin oxide films was evaluated from an ellipsometer, and spectrophotometric transmittances were measured in the wavelength range of 200–800 nm. In the luminous range, the refractive index varied from n=2.36 to 2.04 as oxygen contents increased.