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Physical review. B, Condensed matter

Dephasing in InAs/GaAs quantum dots

Paola Borri, W. Langbein, Jesper Mørk, J. M. Hvam, F. Heinrichsdorff, M. Mao, D. Bimberg

Published Sep 15, 1999• 133 citations
Publisher

Abstract

The room-temperature dephasing in InAs/GaAs self-assembled quantum dots is measured using two independent methods: spectal-hole burning and four-wave mixing. Dephasing times weakly dependent on the excitation density are found, with a low density value of $290\ifmmode\pm\else\textpm\fi{}80 \mathrm{fs}$ from spectal-hole burning and of $260\ifmmode\pm\else\textpm\fi{}20 \mathrm{fs}$ from four-wave mixing.

DOI
10.1103/physrevb.60.7784

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The room-temperature dephasing in InAs/GaAs self-assembled quantum dots is measured using two independent methods: spectal-hole burning and four-wave mixing. Dephasing times weakly dependent on the excitation density are found, with a low density value of 290\ifmmode±\else\textpm\fi80fs290\ifmmode\pm\else\textpm\fi{}80 \mathrm{fs}290\ifmmode±\else\textpm\fi80fs from spectal-hole burning and of 260\ifmmode±\else\textpm\fi20fs260\ifmmode\pm\else\textpm\fi{}20 \mathrm{fs}260\ifmmode±\else\textpm\fi20fs from four-wave mixing.
We have performed time-integrated degenerate four-wave mixing experiments in InAs/GaAs self-assembled quantum dots. The quantum dots are excited in resonance with an intersublevel transition between the valence states of the dots. The dephasing time T2{T}_{2}T2​ is deduced from the time dependence of the photon echo amplitude as a function of the delay between the two incident pulses. At low temperature, a dephasing time T2{T}_{2}T2​ of 15 ps is measured for a resonant excitation at 7.4 \ensuremath{\mu}m wavelength. This dephasing corresponds to an homogeneous broadening of the intersublevel transition of 87 \ensuremath{\mu}eV. The polarization decay time is much longer than the one observed for resonant intersubband excitations in quantum wells. The dephasing time of the intersublevel polarization exhibits only a weak temperature dependence, indicating that the dephasing is not dominated by phonon-assisted scattering mechanisms.
We investigate the dephasing of excitons in InAs self-assembled quantum dots by using a transient four-wave-mixing technique. A used sample is specially designed to compensate the strain. We observe long-lived coherence of excitons at 5 K which corresponds to the dephasing time longer than a nanosecond, where the photon energy of the excitation pulse is 0.874~eV. We find that a pure dephasing due to exciton-phonon interactions dominates in the exciton dephasing rather than the population decay and the exciton-exciton interaction in the weak excitation region, by analyzing the population lifetime and the polarization-dependent dephasing time.
We report on four-wave-mixing experiments in self-assembled InAs/GaAs quantum dots and compare with a theory that accounts for the pure-dephasing induced by acoustic phonons. The measurements demonstrate an unusual non-monotonous temperature dependence of the initial decoherence time in full agreement with previous theoretical predictions made on the basis of a model that concentrates on the lowest electronic states. For samples exhibiting strong electronic confinement this model even yields a good quantitative agreement with the experiments while for less confined samples there are some systematic deviations although many qualitative features are still well reproduced by the model. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
We report a study on temperature-dependent resonant fluorescence from InAs/GaAs quantum dots. We combined spectral and temporal measurements in order to identify sources of dephasing. In the spectral domain, we observed temperature-dependent broadening of the zero-phonon line as $0.3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{eV}/\mathrm{K}$, and a temperature-dependent phonon broadband. Time-resolved autocorrelation measurements revealed temperature-dependent spin pumping times between T1,s=6{T}_{1,s}=6T1,s​=6 ns (4 K) and 0.50.50.5 ns (15 K). These results are compared against theoretical modeling with a master equation for a four-level system coupled to phonon and spin baths. We explained the results by phonon-mediated hole-spin scattering between two excited states, with the piezophonons as a dominant mechanism.
We measured dephasing times in InGaAlAs self-assembled quantum dots at low temperature using degenerate four-wave mixing. At 0 K, the coherence time of the quantum dots is lifetime limited, whereas at finite temperatures pure dephasing by exciton-phonon interactions governs the quantum dot coherence. The inferred homogeneous line widths are significantly smaller than the line widths usually observed in the photoluminescence from single quantum dots indicating an additional inhomogeneous broadening mechanism in the latter.
In this paper we report the dynamic properties of InAs self-assembled quantum dots for spectral hole burning memory applications. We measured the time constant of electron transport between InAs self-assembled quantum dots and the n-GaAs substrate by making use of the frequency dependence of the CV signal due to the InAs dots. We obtained a time constant of 2.1 /spl mu/s from experiments. The experimental results are well explained by equivalent circuit calculations and the theoretically calculated CR time constant. The time constant is expected to reach the sub-picosecond range in samples with a 10 nm barrier thickness.