V. G. Davydov

Coherent Control of Stress-Induced InGaAs Quantum Dots by Means of Phonon-Assisted Resonant Photoluminescence

We report the control of coherent status of the lowest energy electronic state of InGaAs/GaAs stress-induced quantum dots in an inhomogeneously broadened system by time-integrated detection of narrow Raman-like lines in resonant photoluminescence spectra. The dephasing time of 18.5 ps has been found at 2K.

Breakdown of the Phonon Bottleneck Effect in Self-Assembled Quantum Dots

Spectral and temporal behavior of photoluminescence of site-selectively excited InP self-assembled quantum dots were studied in external electric fields. External electric field accelerates the nonradiative relaxation and competing fast phonon mediated relaxation processes make prominent structures in the static spectra. The spectra agree with the time-resolved spectra around the time zero and reflect the phonon relaxation rate. Acoustic phonon mediated carrier relaxation is much faster than predicted theoretically. The increases of the excitation intensity, temperature, electric current and charging of quantum dots accelerate the relaxation of the carriers in quantum dots, indicating build-up of Auger-like processes. This observation demonstrates the breakdown of the predicted phonon bottleneck effect not only at the condition for the practical application of the quantum dots but also at low temperature and under weak excitation.

Increasing of AlGaAs/GaAs quantum well robustness to resonant excitation by lowering Al concentration in barriers

The robustness of AlGaAs/GaAs quantum well to strong resonant excitation is studied. It was found that lowering Al concentration in barriers to 3% does not influence the measured radiative linewidth of exciton resonance in the sample at low intensities. At the same time parasitic broadening of the resonance by an additional resonant illumination is strongly suppressed as compared to the quantum well with 30% of Al in barriers.

Spin Quantum Beats in the Stokes Shifted Photoluminescence of InP Quantum Dots

Quantum beats observed in the photoluminescence kinetics of a single layer of self-assembled quantum dots in a magnetic field are studied as a function of the Stokes shift between the excitation and photoluminescence frequencies in the wide range of Stokes shifts from 7 to 70 meV. The quantum beats are attributed to beats between the fine-structure states of electron-hole pairs.

Quantum Beats in Photoluminescence of InP Quantum Dots in Electric Field

The photoluminescence (PL) kinetics of heterostructures with InP self-assembled quantum dots are studied under quasi-resonant pulse excitation in the presence of an external electric field. An oscillatory behavior of the PL kinetics is shown to arise due to quantum beats of the radiative states. A model of the coherent excitation of nonresonant PL is proposed.

Observation of Franz-Keldysh Oscillations in InP Self-Assembled Quantum Dot Systems

Distinct Franz-Keldysh oscillations were observed in the nonlinear reflection spectra of heterostructures with InP self-assembled quantum dots measured by the pump-probe method. These oscillations showed the presence of a built-in electric field of about 30 kV/cm. The built-in electric field is considered to originate from the electric charge captured by the structural defects on the dot interface. The estimated areal density of the electric charge is about 2×1011 cm-2. Electroreflectance showed nonmonotonic changes with the change in applied bias.

Carrier relaxation dynamics in self-assembled quantum dots studied by artificial control of nonradiative losses

Abstract : A novel technique to study carrier relaxation dynamics based on the artificial control of nonradiative losses by an external electric field is proposed. A clear evidence of phonon assisted relaxation as the main relaxation mechanism of hot electron-hole pairs in InP self-assembled quantum dots is found by the proposed method. Efficient one step relaxation processes with emission of acoustic and optical phonons are observed. These findings give new and important insight into the interaction of the electron-hole pairs in quantum dots with the phono subsystem.

Heterostructure optical phonons in dynamics of quantum dot electronic excitations: new experimental evidences

Unusual coupling of heterostructure optical phonons and electronic excitations in quantum dots (QDs) was observed by photoluminescence spectroscopy in strain-induced InGaAs/GaAs QDs (SIQDs) and self-assembled InAs/GaAs QDs (SAQDs). Phonon-assisted interband transitions in SIQDs were found to be governed by zone center bulk GaAs TO and LO phonons via deformation potential interaction, whereas polar interaction was inessential. For SAQDs, a n-doped GaAs substrate was found to effect on QD intraband relaxation of carriers via coupling between them and substrate LO-phonon-plasmon modes at spacing between QDs and substrate as long as 100 nm.