18 FIG. 9: (Color online) The lowest hole (red/solid contour lines) and electron (blue/dashed contour lines) wave functions in a GaN QD ( t$_{QD}$ = 4 nm ; t$_{inf}$ = t$_{sup}$ = 8 nm). The gray dots are the Al atoms in the AlN barriers. FIG. 8: (Color online) The band gap energy of GaN QDs as a function of the electric field ( t$_{QD}$ = 4 nm). The dotted line is a guide to the eye. The corresponding ( t$_{inf}$ , t$_{sup}$ ) are given (in nm) between parenthesis. The red square is the experimental structure discussed in the text.