  Although there are so many reports on the carrier effective mass (m*) of a
transparent oxide semiconductor BaSnO3, it is almost impossible to know the
intrinsic m* value because the reported m* values are scattered from 0.06 to
3.7 m0. Here we successfully clarified the intrinsic m* of BaSnO3, m*=0.40 0.01
m0, by the thermopower modulation clarification method. We also found the
threshold of degenerate/non-degenerate semiconductor of BaSnO3; At the
threshold, the thermopower value of both La-doped BaSnO3 and BaSnO3 TFT
structure was 240 microvolt k-1, bulk carrier concentration was 1.4E19 cm-3,
and two-dimensional sheet carrier concentration was 1.8E12 cm-2. When the EF
locates above the parabolic shaped conduction band bottom, rather high mobility
was observed. On the contrary, very low carrier mobility was observed when the
EF lays below the threshold, most likely due to that the tail states suppress
the carrier mobility. The present results are useful for further development of
BaSnO3 based oxide electronics.
