Sputtering growth and optical properties of [100]-oriented tetragonal SnO[sub 2] and its Mn alloy films.

SnO[sub 2] and its Mn alloy thin films have been grown on Al[sub 2]O[sub 3](0001) substrates by reactive radio-frequency magnetron sputtering performed in the presence of O[sub 2] gas. The prepared films showed preferred orientation in the [100] direction of the rutile structure of SnO[sub 2]. The O[sub 2]/Ar gas-flow ratio maintained during the sputtering was found to significantly affect the crystalline quality and stoichiometry of the films. The optical constants of the SnO[sub 2] and Sn[sub 1-x]Mn[sub x]O[sub 2] (x<=0.27) films were measured by spectroscopic ellipsometry in the 2–5 eV photon energy region. The band-gap energy of SnO[sub 2] is determined to be 3.86 eV and that of Sn[sub 1-x]Mn[sub x]O[sub 2] increases for x<=0.11 and then decreases for the higher x, exhibiting a negative bowing. The initial increase of the band-gap energy is attributable to the hybridization between localized Mn d states located near the band gap and O p-like valence bands. The decrease of the band-gap energy is interpreted as due to the SnO[sub 2]–MnO[sub 2] alloying effects. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]