A carrier relaxation bottleneck probed in single InGaAs quantum dots using integrated superconducting single photon detectors

Abstract

Using integrated superconducting single photon detectors we probe ultra-slow exciton capture and relaxation dynamics in single self-assembled InGaAs quantum dots embedded in a GaAs ridge waveguide. Time-resolved luminescence measurements performed with on-and off-chip detection reveal a continuous decrease in the carrier relaxation time from 1.22 ± 0.07 ns to 0.10 ± 0.07 ns upon increasing the number of non-resonantly injected carriers. By comparing off-chip time-resolved spectroscopy with spectrally integrated on-chip measurements we identify the observed dynamics in the rise time (τ r ) as arising from a relaxation bottleneck at low excitation levels. From the comparison with the temporal dynamics of the single exciton transition with the on-chip emission signal, we conclude that the relaxation bottleneck is circumvented by the presence of charge carriers occupying states in the bulk material and the two-dimensional wetting layer continuum. A characteristic τ r ∝ P −2/3 power law dependence is observed suggesting Auger-type scattering between carriers trapped in the quantum dot and the two-dimensional wetting layer continuum which circumvents the phonon relaxation bottleneck.Semiconductor based photonic information technology is rapidly being pushed to the quantum limit where single photon states can be generated and manipulated in nanoscale optical circuits 1 . Over recent years quantum dots (QDs) embedded in such semiconductor systems have been shown to be excellent sources of quantum light 2-4 and have shown their suitability for use as a gain medium in QD lasers 5-7 . However, for short response times and fast operation of such devices, injected charge carriers must relax rapidly from continuum wetting layer electronic states into the lasing state. For a fully discrete electronic structure, efficient relaxation is expected to be hindered by phonon bottleneck phenomena 8 , caused by the large energetic spacing of QD energy levels that inhibits single-phonon mediated scattering processes 9 . To directly observe such relaxation bottleneck effects, superconducting single photon detectors (SSPDs) are suitable due to their near unity quantum efficiency and picosecond timing resolution 10,11 . Building up on recent progress in this field 12-14 , we developed highly efficient 15,16 NbNSSPDs on GaAs 17 and demonstrated the monolithic integration of InGaAs QDs as single photon emitters together with waveguides and detectors on a single chip 18 . In this letter, we compare photoluminescence (PL) dynamics recorded from a single dot with confocal off-chip detectors with on-chip PL using integrated SSPDs that provide temporal resolution better than 70 ps. By probing the carrier capture and energy relaxation dynamics

Ultrafast Polariton-Phonon Dynamics of Strongly Coupled Quantum Dot-Nanocavity Systems

“…Hence, we performed the measurements using pulsed resonant excitation and time-resolved detection on a streak camera with sub-5 ps resolution. While non-resonant excitation would lead to slow carrier relaxation into the QDs [31] our resonant scheme minimizes timing jitter in the excitation. To avoid exciting higher rungs of the JC ladder, we pumped the more QD-like polariton branch UP1 (as schematically illustrated by the blue arrow on the right side of figure 1a) with a pulse length that was carefully chosen to be shorter than the state lifetime but spectrally sharp enough not to overlap with the other polariton branch.…”

Integrated superconducting detectors on semiconductors for quantum optics applications

“…A detailed study of the carrier relaxation dynamics in single InGaAs quantum dots probed by onchip integrated SSPDs can be found in Ref. [23].…”

Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage

“…Also, a dependence on relaxation processes in the state preparation results in a timing jitter. In some cases, charge-carrier relaxation times can reach values of up to a nanosecond [23].We present here a coherent technique to create a biexciton with high probability, low jitter, and weak dependence on the * timo.kaldewey@unibas.ch excitation and system parameters. The technique is based on rapid adiabatic passage (RAP).…”

“…Also, a dependence on relaxation processes in the state preparation results in a timing jitter. In some cases, charge-carrier relaxation times can reach values of up to a nanosecond [23].…”