  To clarify the electronic density of states (DOS) around the conduction band
bottom for state of the art transparent amorphous oxide semiconductors (TAOSs),
InGaZnO4 and In2MgO4, we fabricated TAOS-based transparent thin film
transistors (TTFTs) and measured their gate voltage dependence of thermopower
(S). TAOS-based TTFTs exhibit an unusual S behavior. The |S|-value abruptly
increases, but then gradually decreases as Vg increases, clearly suggesting the
anti-parabolic shaped DOS is hybridized with the original parabolic shaped DOS
around the conduction band bottom.
