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Tin dioxide is a large band gap semiconductor, crystallizing in the rutile structure with D4h space group symmetry. Its unit cell is tetragonal and contains two molecules. The calculation of energy bands from first principles for such a crystal of relatively low symmetry and with a large number of valence electrons per unit cell is complicated I 1 to 41. A general description of the band structure in accordance with existing experimental information is still an open problem.To interpret the electrical transport measurement data it is necessary to know the shape of the conduction band, as Sn02 especially in the form of thin film is mostly an n-type semiconductor. In Dlh crystal symmetry, according to the group theory, four energy band models are possible: Experimental investigations of Hall effect, magnetoresistance, and planar Hall effect made by Nagasawa and Shionoya / 5 / indicate that the results can be interpreted in terms of a single spheroidal conduction band model. In general, however, the conduction band being isotropic may not be parabolic. In the case of Sn02, the effective mass of conduction electrons, as will be discussed further, strongly depends on energy indicating the nonparabolicity of the band. The concentration of conduction electrons in the band is influenced by the native defects (oxygen vacancies and interstitial tin ions) and intentionally introduced dopants. For electron concentration greater than lo1' cm-3 Sn02 behaves like a degenerate semiconductor. In that case an impurity band may form. Merging of the impurity band with the parent conduction band can additionally influence the shape of the conduction band.For an energy band with spherical symmetry the energy is assumed to depend solely on the absolute value of the wave vector, the form of this dependence being arbitrary:Wkl, k2, k3) E(k) . .

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