Telecom wavelength single quantum dots with very small excitonic fine-structure splitting

Abstract

We report on molecular beam epitaxy growth of symmetric InAs/InP quantum dots (QDs) emitting at telecom C-band (1.55 µm) with ultra-small excitonic fine-structure splitting of ~2 µeV. The QDs are grown on distributed Bragg reflector and systematically characterized by micro-photoluminescence (µ-PL) measurements. One order of magnitude of QD PL intensity enhancement is observed in comparison with as-grown samples. Combination of power-dependent and polarization-resolved measurements reveal background-free exciton, biexciton and dark exciton emission with resolution-limited linewidth below 35 µeV and biexciton binding energy of ~1 meV. The results are confirmed by statistical measurements of about 20 QDs.

High‐Purity Triggered Single‐Photon Emission from Symmetric Single InAs/InP Quantum Dots around the Telecom C‐Band Window

“…The structure under investigation was grown by MBE on a (100)‐oriented InP substrate . The QDs were formed by depositing nominally two monolayers of InAs on InP at a temperature T = 490 °C combined with the ripening process resulting in low density of symmetric dots (density from 5 × 10 8 to 2 × 10 9 cm −2 in comparison to 6 × 10 9 cm −2 achievable in GaAs‐based structures for the same spectral range). The QDs were placed on a DBR formed by 25 InP/InAlGaAs mirror pairs, for enhancement of the photon extraction efficiency, and were capped by a 100‐nm‐thick InP layer.…”

“…In addition, several matrices/barriers lattice-matched to InP can be considered, which gives additional freedom in modifying the confinement and strain, and hence giving convenient tuning knobs to tailor all the essential single dot characteristic. [26][27][28][29][30][31] There exist approaches able to give a lower spatial density of InAs on InP dots. [32,33] For instance, combining the InP matrix with the double-cap technique in metalorganic chemical vapor deposition (MOCVD) showed high suppression of multiphoton events under non-resonant [34] and quasi-resonant [35,36] excitation.…”

“…Single emission lines in investigated sample are significantly narrower than typically observed for epitaxial nanostructures in this material system, similar to lines A and B (≈43 and ≈38 µeV, respectively). From the comparison to the emission linewidth obtained for a planar structure (the resolution limited linewidth of less than 35 µeV), one may conclude about negligible influence of the charge environmental conditions after fabrication of the mesas suggesting that investigated QDs are relatively far from mesa sidewalls. Moreover, the observed linewidths are comparable to the best observed for GaAs‐based QDs emitting in the 3rd telecom window (≈59 µeV) and are much lower than ≈200 µeV observed for strongly elongated but naturally formed in MBE InAs/InP quantum dashes …”

“…One of the parameters directly affecting QD properties is As‐P exchange process during the growth of QDs. This addresses at once most of the challenges remaining for quantum emitters in the telecom C‐band window: low QD spatial density and in‐plane symmetry as well as the photon extraction efficiency and material quality which has been confirmed by the linewidths of single emission lines well below 50 µeV . However, no single‐photon emission properties for such symmetric InAs/InP QDs have been reported so far, and hence it is the focus of this work aiming to fill this gap.…”

“…This alternative InAs/InP material system is actually the technologically easiest choice because such dots emit naturally in the 1.55 µm range and no special strain engineering has to be applied, which allows overcoming some of the mentioned fabrication drawbacks of the GaAs‐based materials. In addition, several matrices/barriers lattice‐matched to InP can be considered, which gives additional freedom in modifying the confinement and strain, and hence giving convenient tuning knobs to tailor all the essential single dot characteristic . There exist approaches able to give a lower spatial density of InAs on InP dots .…”