  Electrical transport of a polar heterointerface between two insulating
perovskites, KTaO3 and SrTiO3, is studied. It is formed between a thin KTaO3
film deposited on a top of TiO2- terminated (100) SrTiO3 substrate. The
resulting (KO)1-(TiO2)0 heterointerface is expected to be hole-doped according
to formal valences of K (1+) and Ti (4+). We observed electrical conductivity
and mobility in the KTaO3/SrTiO3 similar to values measured earlier in
electron-doped LaAlO3/SrTiO3 heterointerfaces. However, the sign of the charge
carriers in KTaO3/SrTiO3 obtained from the Hall measurements is negative. The
result is an important clue to the true origin of the doping at perovskite
oxide hetero-interfaces.
