  The electronic structure of $p$-type doped \BiTe is studied by angle resolved
photoemission spectroscopy (ARPES) to experimentally confirm the mechanism
responsible for the high thermoelectric figure of merit. Our ARPES study shows
that the band edges are located off the $\Gamma$-Z line in the Brillouin zone,
which provides direct observation that the spin-orbit interaction is a key
factor to understand the electronic structure and the corresponding
thermoelectric properties of \BiTe. Successive time dependent ARPES measurement
also reveals that the electron-like bands crossing E$_F$ near the
$\underline{\Gamma}$ point are formed in an hour after cleaving the crystals.
We interpret these as surface states induced by surface band bending, possibly
due to quintuple inter-layer distance change of \BiTe.
