High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots

This work reports a considerable improvement in the optical quality factor (Q) of GaN-based microdisk (μ-disk) resonators embedding GaN quantum dots (QDs) grown on AlN and AlGaN barriers. Room-temperature photoluminescence (PL) spectroscopy reveals a large number of high-Q whispering gallery modes (WGMs) spanning a wide spectral range (2.6 to 3.4 eV), enabling identification of different radial mode families through comparison with simulations. GaN/AlN QD-based μ-disks demonstrate record-high Q values (Q > 7000 for a 5 μm diameter disk and Q ≈ 5000 for a 2 μm disk), representing the state of the art for nitride photonic structures. The superior performance is attributed to the high etching quality and to the comparatively lower sub-bandgap absorption of QDs with respect to quantum wells.

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