  Here we investigate LaAlO_3-SrTiO_3 heterostructure with\delta-doping of the
interface by LaMnO_3 at less than one monolayer. This doping strongly inhibits
the formation of mobile electron layer at the interface. This results in giant
increase of the resistance and the thermopower of the heterostructure. Several
aspects of this phenomena are investigated. A model to calculate the carrier
concentration is presented and effect of doping and detailed temperature
dependence is analyzed in terms of model parameters and the weak-scattering
theory. The large enhancement of thermopower is attributed to the increased
spin and orbital entropy originating from the LaMnO_3 mono-layer.
