FIG. 10: (Color online) The calculated (TB) and experimental 20 (Exp.) band gap energies of the GaN QDs. Experimental GaN/AlN quantum wells 14 (QW) and Stranski-Krastanov (SK) quantum dots 16 with similar sizes are also reported for comparison. nm) are plotted in Fig. 9. As expected, the electron is confined at the upper interface, while the hole is confined at the lower interface of the QD. The electron and hole are, interestingly, both localized around the axis of the nanowire, where the strains are maximum, hence the piezoelectric field slightly larger than at the surface. This helps preventing one of the carriers from being trapped by the charged lateral surface states. 41 Finally, we compare our theoretical predictions with the experimental results of Ref. 20. In this work, the room-temperature luminescence of 1 to 4 nm thick GaN QDs embedded in 30 nm diameter nanowires showed clear evidence of the quantum confined Stark effect. We have therefore computed the electronic structure of a 1 nm thick QD ( t$_{inf}$ = 10 nm, t$_{sup}$ = 8 nm), of a 2.5 nm thick QD ( t$_{inf}$ = 9 nm, t$_{sup}$ = 10 nm) and of a 4 nm thick QD ( t$_{inf}$ = 8 nm, t$_{sup}$ = 7 nm). The geometry and thickness of the barriers were chosen after a detailed analysis of the experimental TEM images. 56 The calculated and experimental band gap energies are plotted in Fig. 10. All the dots are empty, which is consistent with the observation of the biexciton in the 1 nm thick QDs. 19 The electric field ranges from 5 . 6 MV/cm for t$_{QD}$ = 4 nm to 7 . 3 MV/cm for t$_{QD}$ = 1 nm. It is, as expected, much smaller than in GaN/AlN quantum wells 14 (QWs) and Stranski-Krastanov 16 dots (SKs) with similar 19