Self-aligned photonic defect microcavities with site-controlled quantum dots
Despite the superiority in quantum properties, self-assembled semiconductor quantum dots face challenges in terms of scalable device integration because of their random growth positions, originating from the Stranski-Krastanov growth mode. Even with existing site-controlled growth techniques, for example, nanohole or buried stressor concepts, a further lithography and etching step with high spatial alignment requirements isnecessary to accurately integrate QDs into the nanophotonic devices. Here, we report on the fabrication and characterization of strain-induced site-controlled microcavities where site-controlled quantum dots are positioned at the antinode of the optical mode field in a self-aligned manner without the need of any further nano-processing. We show that the Q-factor, mode volume, height, and the ellipticity of site-controlled microcavities can be tailored by the size of an integrated AlAs/Al2O3 buried stressor, with an opening ranging from 1 to 4 $\mu$m. Lasing signatures, including super-linear input-output response, linewidth narrowing near threshold, and gain competition above threshold, are observed for a 3.6-$\mu$m self-aligned cavity with a Q-factor of 18000. Furthermore, by waiving the rather complex lateral nano-structuring usually performed during the fabrication process of micropillar lasers and vertical-cavity surface emitting lasers, quasi-planar site-controlled cavities exhibit no detrimental effects of excitation power induced heating and thermal rollover. Our straightforward deterministic nanofabrication concept of high-quality quantum dot microcavities integrates seamlessly with the industrial-matured manufacturing process and the buried-stressor techniques, paving the way for exceptional scalability and straightforward manufacturing of high-\b{eta} microlasers and bright quantum light sources.