Self‐Aligned Pillar Arrays Embedding Site‐Controlled Single Quantum Dots for Bright Nonclassical Light Emission

This work presents a practical realization of a foundational approach for fabricating arrays of self‐aligned micro‐ and nanopillar structures incorporating individual site‐controlled quantum dots (QDs) for bright nonclassical light extraction. This method leverages the nonplanar surface morphology of pyramidal QD samples to define dielectric masks self‐aligned to the QD positions. The mask size and consequently the lateral dimensions of the pillars, are precisely controlled through a chemical mechanical polishing (CMP) step, obviating the need for any additional lithography step for creating the pillar. This fabrication technique offers several key advantages, including precise control over the pillar sites, and fully deterministic embedding of QD structures. The functionality of the structures is validated by integrating single In0.25Ga0.75 As QDs—upon two‐photon excitation (TPE) of the biexciton state, the emission of single and polarization‐entangled photon pairs is observed. Additionally, an extra fabrication step to deposit dome‐like structures atop the pillars was demonstrated, resulting in a total light extraction efficiency of 9.5% at the first lens—a record within the pyramidal QD family.