Abstract
Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices. To that end, we create QD single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48%±5% into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50%), low multiphoton probability (g(2)(0) <1%), and a significant Purcell enhancement factor (≈3).
Highlights
Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications
We present a two-colour photoluminescence imaging technique to determine the position of single QDs with respect to fiducial alignment marks, with an average position uncertainty o30 nm obtained for an image acquisition time of 120 s
The simplest photoluminescence imaging configuration we use is a subset of Fig. 1a, and starts with excitation by a 630-nm light emitting diode (LED), which is sent through a 90/10 beamsplitter and through a 20 Â infinity-corrected objective (0.4 numerical aperture) to produce an E200 mm diameter spot on the sample
Summary
Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. Several techniques for location of self-assembled InAs/GaAs QDs before device fabrication have been reported, including atomic force microscopy (AFM)[5], scanning confocal photoluminescence microscopy[6] (including in situ, cryogenic photolithography7,8), photoluminescence imaging[9], and scanning cathodoluminescence[10] Of these approaches, photoluminescence imaging is attractive given its potential to combine high throughput sub-50 nm positioning accuracy, spectral information, and compatibility with high-resolution electronbeam lithography that is typically used to pattern small features such as those used in photonic crystals. This wide-field technique is combined with confocal measurements within the same experimental set-up to determine emission wavelength and polarization We use this information to fabricate and demonstrate QD single-photon sources in a circular Bragg grating geometry that simultaneously exhibit high collection efficiency (48%±5% into a lens with numerical aperture of 0.4), low multiphoton probability at this collection efficiency (g(2)(0) o1%), and a significant Purcell enhancement factor (E3). Our results constitute an important step forward for both the general creation of nanophotonic devices using positioned QDs, and the specific performance of QD single-photon sources
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