We compare the quality factor values of the whispery gallery modes of
microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers
by performing room temperature photoluminescence (PL) spectroscopy. The PL
measurements show a large number of high Q factor (Q) resonant modes on the
whole spectrum which allows us to identify the different radial mode families
and to compare them with simulations. We report a considerable improvement of
the Q factor which reflect the etching quality and the relatively low cavity
loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very
high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks
embedding QDs grown on AlGaN barrier layer. We attribute this difference to the
lower absorption below bandgap for AlN barrier layers at the energies of our
experimental investigation
