Enhanced spectral range of strain-induced tuning of quantum dots in circular Bragg grating cavities

TL;DR

This paper presents a method to significantly improve the strain-induced tunability of quantum dots in circular Bragg grating cavities by filling trenches with a stiff dielectric, combining optical enhancement with effective strain tuning.

Contribution

The study introduces a simple dielectric filling technique that restores nearly full strain tunability in CBG cavities, enabling scalable, bright, and tunable quantum light sources.

Findings

Filling CBG trenches with aluminum oxide restores up to 95% of planar tunability.

Coated devices maintain 98-99% strain-tuning efficiency regardless of underlayer stiffness.

Finite element analysis confirms strain relief causes tunability loss in CBG structures.

Abstract

Tunable sources of entangled and single photons are essential for implementing entanglement-based quantum information protocols, as quantum teleportation and entanglement swapping depend on photon indistinguishability. Tunable devices are fabricated from indium arsenide (InAs) quantum dots (QDs) embedded in gallium arsenide (GaAs) nanomembranes placed on monolithic piezoelectric substrates. Circular Bragg grating (CBG) resonators enhance emission brightness and exploit the Purcell effect; however, the inclusion of CBGs reduces strain-mediated tunability compared to planar nanomembranes. A simple and effective solution is introduced: filling the CBG trenches with a stiff dielectric (aluminum oxide) via atomic layer deposition (ALD) restores up to 95% of the tunability of planar structures. Finite element analysis (FEA) confirms that the tunability loss originates from bending in the device layers due to strain relief in the CBG geometry. Lowering the stiffness of intermediate layers between the QDs and the piezoelectric actuator, such as in bonding or reflector layers, further increases strain losses in uncoated CBGs. Coated devices maintain 98-99% strain-tuning efficiency across all simulated underlayer stiffnesses. The results demonstrate that advantageous optical cavity properties can be effectively combined with piezoelectric strain tuning, enabling scalable, bright, and tunable quantum light sources.