Wet-Etched Microlens Array for 200 nm Spatial Isolation of Epitaxial Single QDs and 80 nm Broadband Enhancement of Their Quantum Light Extraction

Uniform arrays of three shapes ([Formula: see text] , [Formula: see text] , and [Formula: see text]) of GaAs microlenses (MLs) by wet-etching are demonstrated, ∼200 nm spatial isolation of epitaxial single QDs embedded ([Formula: see text]: 890–990 nm) and broadband ([Formula: see text] nm) enhancement of their quantum light extraction are obtained, which is also suitable for telecom-band epitaxial QDs. Combined with the bottom distributed Bragg reflector, the [Formula: see text]-shaped ML forms a cavity and achieves the best enhancement: extraction efficiency of 26%, Purcell factor of 2 and single-photon count rate of [Formula: see text] counts per second at the first lens; while the [Formula: see text]-shaped ML shows a broader band (e.g., longer [Formula: see text]) enhancement. In the MLs, single QDs with featured exciton emissions are observed, whose time correlations prove single-photon emission with multi-photon probability [Formula: see text]; some QDs show both biexciton [Formula: see text] and exciton X emissions and exhibit a perfect cascade feature. This work could pave a step towards a scalable array of QD single-photon sources and the application of QD photon-pair emission for entanglement experiments.