We present a theoretical study of the electron distribution, i.e., two-dimensional electron gas (2DEG) in
polar heterojunctions (HJs) within a realistic model. The 2DEG is confined along the growth direction by
a triangular quantum well with afinite potential barrier and a bent bandfigured by all confinement
sources. Therein, interface polarization charges take a double role: they induce a confining potential and,
furthermore, they can make some change in other confinements, e.g., in the Hartree potential from ionized impurities and 2DEG. Confinement by positive interface polarization charges is necessary for the
ground state of 2DEG existing at a high sheet density. The 2DEG bulk density is found to be increased in
the barrier, so that the scattering occurring in this layer (from interface polarization charges and alloy
disorder) becomes paramount in a polar modulation-doped HJ.