Here we investigate the LaAlO3-SrTiO3 heterostructure with δ-doping of the interface by LaMnO3 at less than one monolayer. This doping strongly inhibits the formation of a mobile electron layer at the interface. This results in a 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 the effect of doping with detailed temperature dependence is analyzed in terms of model parameters and weak-scattering theory. The large enhancement of the thermopower is attributed to the increased spin and orbital entropy originating from the LaMnO3 monolayer. © Copyright EPLA, 2014.