  III-nitride-on-silicon L3 photonic crystal cavities with resonances down to
315 nm and quality factors (Q) up to 1085 at 337 nm have been demonstrated. The
reduction of the quality factor with decreasing wavelength is investigated.
Besides the quantum well absorption below 340 nm, a noteworthy contribution is
attributed to the residual absorption present in thin AlN layers grown on
silicon, as measured by spectroscopic ellipsometry. This residual absorption
ultimately limits the Q factor to around 2000 at 300 nm when no active layer is
present.
