Deterministic positioning of circular Bragg gratings using atomic force lithography for high-performance quantum dot light sources

TL;DR

This paper introduces a room-temperature AFM-assisted lithography technique for precisely positioning quantum dots within circular Bragg gratings, significantly enhancing photoluminescence and device stability for quantum light sources.

Contribution

The authors demonstrate a scalable, deterministic method for integrating quantum dots with photonic cavities using AFM nano-oxidation lithography, achieving high precision and device performance.

Findings

Achieved a radial displacement of 51(28) nm for QD positioning.

Observed a 245-fold photoluminescence enhancement in devices.

Maintained stable FSS and polarization imbalance below 5% for displacements up to 50 nm.

Abstract

Semiconductor quantum dots (QDs) grown by molecular beam epitaxy are excellent quantum emitters, but their random spatial distribution hinders deterministic coupling to optical microcavities. We demonstrate a room-temperature atomic force microscopy (AFM)-assisted nano-oxidation lithography technique enabling QD positioning with a radial displacement of $51(28)$ nm. Free-standing asymmetric circular Bragg gratings incorporating AFM-positioned GaAs QDs exhibit a $245$-fold photoluminescence enhancement and fine-structure splitting (FSS) comparable to bulk QDs. Polarization-resolved spectroscopy and finite-difference time-domain simulations show robust emission for displacements up to $50$ nm (Stokes parameter $\lvert S \rvert < 0.05$ ). The devices display stable FSS and polarization imbalance below $5 \, \%$ , confirming precise, reproducible alignment and potential for high fidelity devices. This scalable approach enables deterministic integration of high-performance QDs with photonic cavities, advancing practical quantum light sources for quantum information technologies.