Microphotoluminescence studies on GaN-based airpost pillar microcavities containing InGaN quantum wells and quantum dots

We report on the optical properties of monolithic GaN‐based airpost pillar microcavities (MCs) with embedded InGaN quantum wells or quantum dots (QDs), respectively. The presented MCs are designed by use of different kinds of distributed Bragg reflectors consisting of either AlGaN/GaN, AlInN/GaN, or superlattices of AlN/InGaN and GaN. A quality factor of up to Q = 260 has been achieved. Airpost pillar MCs, providing a three‐dimensional optical confinement, are realized by focused ion beam etching starting from an all‐epitaxially grown vertical‐cavity surface‐emitting laser structure. Pillar diameters below 1 µm are well controllable. The sidewalls are smooth and show a damaged surface layer of a thickness less than 2 nm only. Microphotoluminescence (µ‐PL) measurements reveal the longitudinal and transversal mode spectra of the cavities in good agreement with theoretical calculations based on a vectorial transfer‐matrix method. Furthermore, the spectra of the QD based samples reveal distinct spectrally sharp emission lines around 2.73 eV which can be attributed to the emission of single‐InGaN QDs and traced up to 120 K. Scanning electron micrograph of a GaN‐based airpost pillar superimposed by the µ‐PL spectrum of a pillar with a diameter of d = 1.8 µm. The measurement performed at T = 150 K reveals the discrete resonator modes.