We present atomistic computations within an empirical pseudopotential framework for the electron $s$-shell ground state $g$ tensor of InGaAs quantum dots (QDs) embedded to host matrices that grant electronic confinement. A large structural set consisting of geometry, size, and molar fraction variations is worked out which also includes a few representative uniform strain cases. The tensor components are observed to display insignificant discrepancies even for the highly anisotropic shapes. The family of $g$-factor curves associated with these parameter combinations coalesces to a single universal one when plotted as a function of the gap energy, thus confirming a recent assertion reached under much restrictive conditions. Our work extends its validity to alloy QDs with various shapes and finite confinement that allows for penetration to the host matrix, placing it on a more realistic basis. Accordingly, the electrons in InGaAs QDs having $s$-shell transition energies close to 1.13 eV will be least susceptible to magnetic field. We also show that low indium concentration offer limited $g$-factor tunability under shape or confinement variations. These findings can be taken into consideration in the fabrication and the use of InGaAs QDs with $g$-near-zero or other targeted $g$ values for spintronic or electron spin resonance-based direct quantum logic applications.
We demonstrate experimental results based on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the internal quantum efficiency (IQE) of InGaAs quantum dots (QDs). Using a strain-reducing layer (SRL) these QDs can be employed for the manufacturing of single-photon sources (SPS) emitting in the telecom O-Band. The OS and IQE are evaluated by determining the radiative and non-radiative decay rate under variation of the optical density of states at the position of the QD as proposed and applied in J. Johansen et al. Phys. Rev. B 77, 073303 (2008) for InGaAs…
We study the effects of the nonlinear piezoelectricity and the In distribution on the exciton energy, the electron-hole electric dipole moment, and the fine-structure splitting in stress-tunable InGaAs/GaAs quantum dots integrated onto a piezoelectric actuator. In particular, we investigate in detail the contributions of various elements of the expansion of the electrical polarization in terms of externally induced elastic strain on the latter two important quantum dot properties. Based on the comparison of the effects of first- and second-order piezoelectricity we provide a simple relation to…
Molecular beam epitaxy of wafer-scale O-band InAs/InGaAs quantum dots on GaAs for quantum photonics
Technical University of Munich（慕尼黑工业大学）；TUM School of Computation, Information and Technology, Technical University of Munich（慕尼黑工业大学计算、信息与技术学院）；Julius-Maximilians-Universität Würzburg（维尔茨堡大学）；Saqura Technologies GmbH（萨库拉技术有限公司）；Ruhr University Bochum（波鸿鲁尔大学）；Ludwig-Maximilians-University Munich（慕尼黑大学）；Technical University Berlin（柏林工业大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）
The electronic structure of strain-engineered single InGaAs/GaAs quantum dots emitting in the telecommunication O band is probed experimentally by photoluminescence excitation spectroscopy. Observed resonances can be attributed to p-shell states of individual quantum dots. The determined energy difference between s-shell and p-shell shows an inverse dependence on the emission energy. The experimental data are compared with the results of confined states calculations, where the impact of the size and composition in the investigated structures is simulated within the 8-band $\mathbf{k}\cdot\math…
In this paper, we study the exciton absorption spectra in InGaAs prolate ellipsoidal quantum dots when a strong pump laser resonant with electron quantized levels is active. Our obtained results by renormalized wavefunction theory show that, under suitable conditions, the initial exciton absorption peak is split into two new peaks as the evidence of the existence of the three-level optical Stark effect of excitons. We have suggested an explanation of the origin of the effect as well as investigating the effect of pump field energy, size, and geometric shape of the quantum dots on effect charac…
Trion quantum coherence in site-controlled pyramidal InGaAs quantum dots
Department of Physics, University of Strathclyde（斯特拉斯克莱德大学物理系）；Sussex Centre for Quantum Technologies, University of Sussex（苏塞克斯大学苏塞克斯量子技术中心）；Tyndall National Institute, University College Cork（科克大学学院廷德尔国家研究所）
The so called "incomplete hole shell filling" phenomenon, that is the breaking of the Aufbau principle was reported by D. Reuter et al., [Phys. Rev. Lett. 94, 026808] in the hole charging spectra of quantum dot when results were interpreted in context of s/p/d shell system - typical for electrons. We report an example of inter-particle-interaction induced Aufbau principle violation even if it is applied to one-particle Kohn-Luttinger eigenstates. We present a k-dot-p/configuration-interaction study that concerns multiple holes confined in InGaAs/GaAs self-assembled cylindrical quantum dot. Eig…
The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology transfer to telecom wavelengths. As an example, we fabricate and characterize especially designed photonic structures with strain-engineered single InGaAs/GaAs quantum dots that are deterministically integra…
Quantum dots are arguably one of the best platforms for optically accessible spin based qubits. The paramount demand of extended qubit storage time can be met by using quantum-dot-confined dark exciton: a longlived electron-hole pair with parallel spins. Despite its name the dark exciton reveals weak luminescence that can be directly measured. The origins of this optical activity remain largely unexplored. In this work, using the atomistic tight-binding method combined with configuration-interaction approach, we demonstrate that atomic-scale randomness strongly affects oscillator strength of d…
The electron-phonon coupling in self-assembled InGaAs quantum dots is relatively weak at low light intensities, which means that the zero-phonon line in emission is strong compared to the phonon sideband. However, the coupling to acoustic phonons can be dynamically enhanced in the presence of an intense optical pulse tuned within the phonon sideband. Recent experiments have shown that this dynamic vibronic coupling can enable population inversion to be achieved when pumping with a blue-shifted laser and for rapid de-excitation of an inverted state with red detuning. In this paper we confirm th…
We study Rabi rotations arising in intensity-dependent photon echoes from an ensemble of self-assembled InGaAs quantum dots. To achieve a uniform distribution of intensities within the excited ensemble, we introduce flattop intensity profiles of picosecond laser pulses. This allows us to overcome the damping of Rabi rotations imposed by the spatial inhomogeneity of Rabi frequencies by a Gaussian laser profile. Using photon echo polarimetry, we distinguish between the coherent optical responses from exciton and trion ensembles. Here, we demonstrate that a photo-induced charging of the quantum d…
We investigated optical spin orientation and dynamic nuclear polarization (DNP) in individual self-assembled InGaAs/GaAs quantum dots (QDs) doped by a single Mn atom, a magnetic impurity providing a neutral acceptor A$^0$ with an effective spin $J=1$. We find that the spin of an electron photo-created in such a quantum dot can be efficiently oriented by a quasi-resonant circularly-polarized excitation. For the electron spin levels which are made quasi-degenerate by a magnetic field compensating the exchange interaction $Δ_e$ with A$^0$, there is however a full depolarization due the anisotropi…
AlGaAs nanowires as a universal platform for GaAs, InGaAs, and InAs quantum dots
Technical University of Denmark（丹麦技术大学）；St. Petersburg State University（圣彼得堡国立大学）；Université Paris Saclay（巴黎萨克雷大学）；CNRS（法国国家科学研究中心）；Alferov University（阿尔费罗夫大学）
Hereby, we present a comprehensive experimental and theoretical study of the electronic structure and optical properties of excitonic complexes in strain-engineered InGaAs/GaAs quantum dots (QDs) grown by metal-organic chemical vapour deposition and emitting at the 1300 nm telecommunication window. Single QD properties have been determined experimentally for a number of nanostructures by means of excitation-power-dependent and polarization-resolved microphotoluminescence and further compared with the results of confined states calculations employing the 8-band kp theory combined with the confi…
The GaAs-based material system is well-known for the implementation of InAs quantum dots (QDs) with outstanding optical properties. However, these dots typically emit at a wavelength of around 900nm. The insertion of a metamorphic buffer (MMB) can shift the emission to the technologically attractive telecom C-band range centered at 1550nm. However, the thickness of common MMB designs limits their compatibility with most photonic resonator types. Here we report on the MOVPE growth of a novel InGaAs MMB with a non-linear indium content grading profile designed to maximize plastic relaxation with…
Photoluminescence polarization is experimentally studied for samples with (In,Ga)As/GaAs selfassembled quantum dots in transverse magnetic field (Hanle effect) under slow modulation of the excitation light polarization from fractions of Hz to tens of kHz. The polarization reflects the evolution of strongly coupled electron-nuclear spin system in the quantum dots. Strong modification of the Hanle curves under variation of the modulation period is attributed to the peculiarities of the spin dynamics of quadrupole nuclei, which states are split due to deformation of the crystal lattice in the qua…
The Stranski-Krastanov (SK) growth-mode facilitates the self-assembly of quantum dots (QDs) using lattice-mismatched semiconductors, for instance InAs and GaAs. SK QDs are defect-free and can be embedded in heterostructures and nano-engineered devices. InAs QDs are excellent photon emitters: QD-excitons, electron-hole bound pairs, are exploited as emitters of high quality single photons for quantum communication. One significant drawback of the SK-mode is the wetting layer (WL). The WL results in a continuum rather close in energy to the QD-confined-states. The WL-states lead to unwanted scatt…
Optical and electronic properties of symmetric InAs/InGaAlAs/InP quantum dots formed by a ripening process in molecular beam epitaxy: a promising system for broad-range single-photon telecom emitters
The Zeeman-split spin-states of a single electron confined in a self-assembled quantum dot provide an optically-accessible spin qubit. For III-V materials the nuclear spins of the solid-state host provide an intrinsic noise source, resulting in electron-spin dephasing times of few nanoseconds. While a comprehensive study of electron-spin dynamics at low magnetic field has recently been carried out, what limits the electron coherence in these systems remains unclear, in part due to the dominant effect of measurement-induced dynamic polarisation of the nuclear bath. We develop an all-optical met…
The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study 3-pulse spin-dependent photon echoes subject to moderate transverse magnetic …
We present here an atomistic theory of the electronic and optical properties of hexagonal InAsP quantum dots in InP nanowires in the wurtzite phase. These self-assembled quantum dots are unique in that their heights, shapes, and diameters are well known. Using a combined valence-force-field, tight-binding, and configuration-interaction approach we perform atomistic calculations of single-particle states and excitonic, biexcitonic and trion complexes as well as emission spectra as a function of the quantum dot height, diameter and As versus P concentration. The atomistic tight-binding parameter…
