  Cathodoluminescence measurements on single InGaN/GaN quantum dots (QDs) are
reported. Complex spectra with up to five emission lines per QD are observed.
The lines are polarized along the orthogonal crystal directions [1 1 -2 0] and
[-1 1 0 0]. Realistic eight-band k.p electronic structure calculations show
that the polarization of the lines can be explained by excitonic recombinations
involving hole states which are either formed by the A or the B valence band.
