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We present microwave frequency measurements of the dynamic admittance of a quantum dot tunnel-coupled to a two-dimensional electron gas. The measurements are made via a high-quality 6.75 GHz on-chip resonator capacitively coupled ...
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We present microwave frequency measurements of the dynamic admittance of a quantum dot tunnel-coupled to a two-dimensional electron gas. The measurements are made via a high-quality 6.75 GHz on-chip resonator capacitively coupled to the dot. The resonator frequency is found to shift both down and up close to conductance resonance of the dot corresponding to a change of sign of the reactance of the system from capacitive to inductive. The observations are consistent with a scattering matrix model. The sign of the reactance depends on the detuning of the dot from conductance resonance and on the magnitude of the tunnel rate to the lead with respect to the resonator frequency. Inductive response is observed on a conductance resonance when tunnel coupling and temperature are sufficiently small compared to the resonator frequency.
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We have carried out continuous wave and time resolved photoluminescence experiments in self-assembled In(Ga)As quantum dots and quantum rings embedded in field effect structure devices. In both kinds of nano-structures, we find a ...
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We have carried out continuous wave and time resolved photoluminescence experiments in self-assembled In(Ga)As quantum dots and quantum rings embedded in field effect structure devices. In both kinds of nano-structures, we find a noticeable increase of the exciton radiative lifetime with the external voltage bias that must be attributed to the field-induced polarizability of the confined electron hole pair. The interplay between the exciton radiative recombination and the electronic carrier tunneling in the presence of a stationary electric field is therefore investigated and compared with a numerical calculation based on the effective mass approximation.
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Formation and evolution of a multimodal InAs/GaAs quantum dot (QD) ensemble during a growth interruption prior to cap layer deposition is studied. These particular kinds of QDs form self-organized after deposition of an InAs layer...
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Formation and evolution of a multimodal InAs/GaAs quantum dot (QD) ensemble during a growth interruption prior to cap layer deposition is studied. These particular kinds of QDs form self-organized after deposition of an InAs layer close to the critical thickness for elastic relaxation and after a short growth interruption. The QDs consist of pure InAs with heights varying in steps of complete InAs monolayers, have well-defined, flat, top and bottom interfaces, and show indications for steep side facets in transmission electron micrographs. QDs with a common height represent a subensemble within the QD ensemble, showing an emission peak with small inhomogeneous broadening. The evolution occurs by an increased appearance of subensembles with higher QDs and disappearance of subensembles related to smaller QDs, which accordingly dissolve. Dissolution proceeds essentially by a decrease of height, and only to a small amount by lateral shrinking. Thickness and composition of the wetting layer do not change during this process; growth and dissolution originate solely from material exchange between different QD subensembles. The evolution slows down for prolonged growth interruption, but the QD ensemble does not attain equilibrium within a time scale of minutes being eventually limited by the onset of plastic relaxation. Formation and dynamics of the observed evolution of the multimodal QD size distribution is theoretically well described by a kinetic approach, which implies strain-controlled adatom kinetics in the mass exchange between the QDs mediated by the adatom sea.
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We have developed a three-dimensional model for electronic states calculation of interdiffused quantum dots (QDs) with arbitrary shape by solving the BenDaniel-Duke's equation in momentum space domain. The proposed model features ...
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We have developed a three-dimensional model for electronic states calculation of interdiffused quantum dots (QDs) with arbitrary shape by solving the BenDaniel-Duke's equation in momentum space domain. The proposed model features several advantages such as automatic solution to the Fick's diffusion equation, a relatively compact and efficient Hamiltonian matrix, and natural representation of a large array of QDs. Without considering the interdiffusion effect, our model yields good agreement with our references of InAs/GaAs QDs ground state energy calculation. We analyze the interdiffusion effect in QDs with various shapes of theoretical and practical interest like spherical, cubical, pyramidal, and lens shaped. We study the effect of QD size and aspect ratio to the blueshift profile due to interdiffusion. We found a similar blueshift profile in these QDs at almost any size that can be well approximated by sech(x) function. This model will serve as a valuable tool for QD band gap engineering based on the interdiffusion technique.
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Semiconductor quantum dots driven by the broadband radiation fields of nearby quantum point contacts provide an interesting setting for probing dynamics in driven quantum systems at the nanoscale. We report on real-time charge-sen...
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Semiconductor quantum dots driven by the broadband radiation fields of nearby quantum point contacts provide an interesting setting for probing dynamics in driven quantum systems at the nanoscale. We report on real-time charge-sensing measurements of the dot occupation, which reveal sharp resonances in the ionization rate as a function of gate voltage and applied magnetic field. Despite the broadband nature of excitation, the resonance widths are much smaller than the scale of thermal broadening. We show that such resonant enhancement of ionization is not accounted for by conventional approaches relying on elastic scattering processes, but can be explained via a mechanism based on a bottleneck process that is relieved near excited state level crossings. The experiment thus reveals a regime of a strongly driven quantum dynamics in few-electron systems. The theoretical results are in good agreement with observations.
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Quantum dot (QD) blinking is characterized by switching between an "on" state and an "off" state, and a power-law distribution of on and off times with exponents from 1.0 to 2.0. The origin of blinking behavior in QDs, however, ha...
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Quantum dot (QD) blinking is characterized by switching between an "on" state and an "off" state, and a power-law distribution of on and off times with exponents from 1.0 to 2.0. The origin of blinking behavior in QDs, however, has remained a mystery. Here we describe an energy-band model for QDs that captures the full range of blinking behavior reported in the literature and provides new insight into features such as the gray state, the power-law distribution of on and off times, and the power-law exponents.
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The homogeneous broadening in semiconductor quantum dot (QD) lasers and optical amplifiers is studied theoretically. Based on a model for the electronic states of the coupled QD-wetting layer (WL) system, Coulomb interaction matri...
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The homogeneous broadening in semiconductor quantum dot (QD) lasers and optical amplifiers is studied theoretically. Based on a model for the electronic states of the coupled QD-wetting layer (WL) system, Coulomb interaction matrix elements are calculated, including both screening and exchange interaction. The homogeneous broadening due to various Auger processes, involving scattering of carriers between WL states and confined QD states, is calculated. The effects of the orthogonalization of WL states, QD confinement, QD density, and carrier density on the homogeneous broadening are studied systematically. We found that such WL-assisted Auger scattering is very efficient with subpicosecond dephasing times, and it is the dominant channel for the homogeneous broadening at high carrier density. Good agreement is achieved when comparing our theoretical results and recent experimental data.
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We present a study of photoelectrical properties of the Stranski-Krastanow InAs quantum dots embedded in an InGaAs matrix with low In content, emitting at about 1.3 μm. The ground-state electron-hole transition of the dots was in...
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We present a study of photoelectrical properties of the Stranski-Krastanow InAs quantum dots embedded in an InGaAs matrix with low In content, emitting at about 1.3 μm. The ground-state electron-hole transition of the dots was investigated as a function of the temperature in presence of electric fields parallel and perpendicular to the plane of the dots by pho-tocurrent spectroscopy. Microphotoluminescence measurements were also carried out, allowing us to evidence carrier capture from the GaAs matrix into the dots.
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The emission cascade of a single quantum dot is a promising source of entangled photons. A prerequisite for this source is the use of a symmetric dot analogous to an atom in a vacuum, but the simultaneous achievement of structural...
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The emission cascade of a single quantum dot is a promising source of entangled photons. A prerequisite for this source is the use of a symmetric dot analogous to an atom in a vacuum, but the simultaneous achievement of structural symmetry and emission in a telecom band poses a challenge. Here we report the growth and characterization of highly symmetric InAs/InAlAs quantum dots self-assembled on C_(3v) symmetric InP(111)A. The broad emission spectra cover the O (λ ～ 1.3 μm), C (λ ～ 1.55 μm), and L (λ ～ 1.6 μm) telecom bands. The distribution of the fine-structure splittings is considerably smaller than those reported in previous works on dots at similar wavelengths. The presence of dots with degenerate exciton lines is further confirmed by the optical orientation technique. Thus, our dot systems are expected to serve as efficient entangled photon emitters for long-distance fiber-based quantum key distribution.
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Photoluminescence and excitation of the photoluminescence spectroscopy has been performed in single InGaAs self-assembled quantum rings embedded in a field effect structure device. To determine their electronic structure, bias-dep...
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Photoluminescence and excitation of the photoluminescence spectroscopy has been performed in single InGaAs self-assembled quantum rings embedded in a field effect structure device. To determine their electronic structure, bias-dependent optical transitions have been analyzed both, for individual quantum rings, and for the averaged ensemble. Our results are compared with a theoretical model, and also with results reported by other authors studying similar nanostructures.
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