Unconventional quantum-confined Stark effect in a single GaN quantum dot

We show that a peculiar excitonic effect and a confining potential in self-assembled hexagonal GaN/AlN quantum dots produce an unconventional quantum-confined Stark effect. In contrast to the conventional quantum-confined Stark shift, the emission line from a single GaN dot under the applied electric field perpendicular to the growth direction blueshifts nearly symmetrically with respect to the direction of the field. The field dependence of the emission lines is reproduced in a charge self-consistent effective mass calculation, taking into account strain, piezoelectric charge, and pyroelectric charge. The unconventional blueshift is attributed to a significant variation of the exciton binding energy, made obvious by a cancellation between the energy shifts of electron and hole confined states.