Bright and Highly Uniform, Pure, Indistinguishable, Spatially-Ordered Single Quantum Dot Emitters—Molecular Beam Epitaxial Growth and Structural Characterization

A significant step forward in the long-sought goal of on-chip quantum optical circuits is the development of spatially-ordered and spectrally highly uniform and pure single photon emitters provided by a unique class of shape and size controlled single quantum dots, dubbed mesa-top single quantum dots (MTSQDs [1,2]). Quantum dots are the only known solid-state on-demand single photon emitters that have been shown to intrinsically exceed all required quantitative figures-of-merit known for realizing on-chip networks aimed at linear optical quantum computing (LOQC), secure high-capacity quantum communication, and multi-photon entangled states as a basic quantum resource for quantum information processing. The realization of spatially-ordered scalable arrays of MTSQDs while maintaining individual QD characteristics above the threshold [1,4] has thus paved the way for the fabrication and study of quantum optical networks. In this talk we report on (i) the molecular beam epitaxial growth of these remarkable MTSQDs based on the underlying physics of the substrate-encoded size-reducing epitaxy (SESRE) on patterned substrates with judiciously chosen scalable nanomesa arrays, and (ii) their structural and compositional character as determined by scanning transmission electron microscopy (STEM) [4]. The demonstrated uniformity and reproducibility of the SPS characteristics is, for the first time, shown to arise from the unprecedented control on shape, size, and composition of the individual quantum dots across the arrays. Equally significant, such quality is controlled from run-to-run when guided by RHEED-based machine condition transfer function as we demonstrate here.<br/>The SESRE approach enables the formation of single quantum dots of controlled shape and size on mesa-tops for both lattice matched (GaAs/AlGaAs) and lattice mismatched (InGaAs/AlGaAs) material systems. Results of STEM studies provide (i) evolution of the growth front profile through the stages of as-patterned nanomesa size-reduction, deposition of the SQD, and continued growth of the morphology planarizing overlayer; (ii) evidence for the unprecedented control over size and shape uniformity of epitaxial QDs underpinning the spectral uniformity emission (&lt;3nm) across the arrays [1,4]; (iii) control of SQD lateral positions to an accuracy of &lt;10nm. The planarization of the MTSQDs [3] makes them naturally suitable for horizontal on-chip integration with light manipulating units (cavity, waveguide, directional coupler) using either standard monolithic integration or hybrid integration with silicon photonics. The MTSQD arrays thus pave the way as a unique platform of quantum emitters for realizing the long-sought on-chip QOCs.<br/><br/>The work is supported by the US Army Research Office (W911NF1910025) and the Air Force Office of Scientific Research (FA9550-17-1-0353).<br/><br/>[1] J. Zhang, arXiv:2108.01428 (2021).<br/>[2] J. Zhang et al., Jour. App. Phys. <b>120</b>, 243103 (2016)<br/>[3] J. Zhang, et al., APL photonics <b>5</b>, 116106 (2020)<br/>[4] J. Zhang et al. [Under Review]