Figure 1.

a Internal polarization field causes separation in the carrier wave function centers and charge separation. b As carrier density increases the electric field is shielded (reduced) at the center of the well and most of the potential drop occurs near the edges. Wave fucntions are localized at the edges. The energy level separation increases (blue shifts) with increasing wave function confinement (constriction). c At even higher densities the electric field is completely shielded at the center and the voltage drop is localized at nanometer-width charged layers (plasma sheaths). Eventually the energy level is pushed above the edge-well depth V_o and the wave function expands to occupy the entire QW width, for a complete “rectification” of the QCSE