Exciton Binding Energies in Zincblende GaN/AlGaN Quantum Wells

The exciton binding energies for the zincblende (ZB) GaN/AlGaN quantum well (QW) structure are investigated within the framework of effective mass theory. These results are also compared with those of the wurtzite (WZ) GaN/AlGaN QW structure. The flat-band model reveals that the exciton binding energy of the ZB structure is much smaller than that of the WZ structure. However, with the inclusion of an internal field due to the piezoelectric (PZ) and spontaneous (SP) polarizations, the exciton binding energy of the WZ structure is largely reduced and comparable to that of the ZB structure. The ZB structure reveals that, with decreasing well width, the exciton binding energy decreases because the envelope function spreads into the barrier region. On the other hand, the self-consistent model of the WZ structure reveals that the exciton binding energy largely increases with decreasing well width. In the case of the Al composition dependence, the exciton binding energies for both ZB and WZ structures are shown to be nearly independent of the Al composition. It is found that the exciton binding energy is significantly reduced with increasing sheet carrier density, suggesting that excitons are nearly bleached at densities around 10¹²cm^-2.