Piezoelectric and spontaneous polarization effects on exciton binding energies in wurtzite GaN/AlGaN quantum wells

Piezoelectric and spontaneous polarization effects on the exciton binding energies of the GaN/Al_xGa_1-xN quantum well (QW) structure are investigated as functions of the well width and the Al composition in the barrier by using a self-consistent (SC) calculation. In the case of a very narrow QW, no significant difference between the SC model and the flat-band (FB) model without polarizations is observed in the exciton binding energy. For the QW with a large well width, on the other hand, the exciton binding energy in the SC model is remarkably reduced compared to that in the FB model. This results from a smaller overlap due to the spatial separation between the conduction and the valence wave functions as the well width gets larger. The exciton binding energy is also found to be nearly independent of the Al composition.