A simple model of circular polarization dependence on Mn delta-layer position in LED heterostructures with InGaAs/GaAs quantum well is proposed, being able to explain quite accurately recent fascinating experimental results [S.V. Zaitsev, et al., Physica E (2009), doi:10.1016/j.physe.2008.11.003]. The model emphasizes the role of position-dependent exchange interaction between injected holes and Mn spins which significantly affects the hole level splitting in a magnetic field, leading to strong variations of polarization dependence. The role of effective temperature corresponding to the injected hole energy and the broadening caused by the geometrical structure imperfections is also discussed.
Time-resolved Kerr rotation spectroscopy as a function of pump-probe distance, voltage and magnetic field is used to measure the momentum-dependent spin splitting energies in GaAs and InGaAs epilayers. The strain of the samples can be reproducibly controlled in the cryostat using three- and four-point bending applied with a mechanical vise. We find that the magnitude of the spin splitting increases linearly with applied tension and voltage. A strain-drift diffusion model is used to relate the magnitude of the measured spin-orbit splitting to the amount of strain in the sample.
We present an analysis of gated InGaAs/InAlAs heterostructures, a device platform to realize spinorbitronic functionalities in semiconductors. The phenomenological model deduced from our magnetotransport experiments allows us to correlate the gate response of the studied two-dimensional electron systems to heterostructure design parameters, in particular the indium concentration. We explain the occurrence of metastable electrostatic configurations showing reduced capacitive coupling and provide gate operation strategies to reach classical field effect control in such heterostructures. Our stud…
We investigate the zero and finite temperature transport properties of a quasi-two-dimensional electron gas in a GaAs/InGaAs/GaAs quantum well under a magnetic field, taking into account many-body effects via a local-field correction. We consider the surface roughness, roughness-induced piezoelectric, remote charged impurity and homogeneous background charged impurity scattering. The effects of the quantum well width, carrier density, temperature and local-field correction on resistance ratio are investigated. We also consider the dependence of the total mobility on the multiple scattering eff…
We report on efficient spin injection in p-doped InGaAs/GaAs quantum-dot (QD) spin light emitting diode (spin-LED) under zero applied magnetic field. A high degree of electroluminescence circular polarization (Pc) ~19% is measured in remanence up to 100K. This result is obtained thanks to the combination of a perpendicularly magnetized CoFeB/MgO spin injector allowing efficient spin injection and an appropriate p-doped InGaAs/GaAs QD layer in the active region. By analyzing the bias and temperature dependence of the electroluminescence circular polarization, we have evidenced a two-step spin r…
The electric conductivity behavior in the single and double tunnel-coupled quantum wells (QW) with different doping profile caused by impact of short pulses of the strong longitudinal (in the quantum wells plane) electric field has been investigated. It is established that at low temperatures (4 K) after such impact the long-term metastable state with increased electric conductance may be observed in the case of the asymmetric QW couple with the impurity delta shaped layer in the narrower QW. It is not observed in the structures with other configurations. The observed effect is explained by th…
Time-resolved Faraday rotation is used to measure the coherent electron spin precession in a GaAs/InGaAs quantum well below an interdigitated magnetized Fe grating. We show that the electron spin precession frequency can be modified by applying a gate voltage of opposite polarity to neighboring bars. A tunability of the precession frequency of 0.5 GHz/V has been observed. Modulating the gate potential with a gigahertz frequency allows the electron spin precession to be controlled on a nanosecond timescale.
Photoluminescence (PL) and reflectivity spectra of a high-quality InGaAs/GaAs quantum well structure reveal a series of ultra-narrow peaks attributed to the quantum confined exciton states. The intensity of these peaks decreases as a function of temperature, while the linewidths demonstrate a complex and peculiar behavior. At low pumping the widths of all peaks remain quite narrow ($< 0.1$ meV) in the whole temperature range studied, $4 - 30K$. At the stronger pumping, the linewidth first increases and than drops down with the temperature rise. Pump-probe experiments show two characteristic ti…
Shallow GaAs/InGaAs/GaAs quantum well structures with and without a three monolayer thick AlAs central barrier have been investigated for different well widths and Si doping levels. The transport parameters are determined by resistivity measurements in the temperature range 4-300 K and magnetotransport in magnetic fields up to 12 T. The (subband) carrier concentrations and mobilities are extracted from the Hall data and Shubnikov-de Haas oscillations. We find that the transport parameters are strongly affected by the insertion of the AlAs central barrier. Photoluminescence spectra, measured at…
Carrier dynamics of submonolayer (SML) InGaAs/GaAs quantum dots (QDs) were studied by micro-photoluminecence (MPL), selectively excited photoluminescence (SEPL), and time-resolved photoluminescence (TRPL). MPL and SEPL show the coexistence of localized and delocalized states, and different local phonon modes. TRPL reveal shorter recombination lifetimes and longer capture times for the QDs with higher emission energy. This suggests that the smallest SML QDs are formed by perfectly vertically correlated 2D InAs islands, having the highest In content and the lowest emission energy, while a slight…
We study the electronic and optical properties of laterally coupled InGaAs/GaAs quantum dot molecules under lateral electric field. We find that electrons perceive the double-dot structure as a compound single object, while the holes discern two well separated dots. Through a combination of predictive atomistic modeling, detailed morphology studies, and single object micro-photoluminescence measurements, we show that this peculiar confinement results in an unusual heterogeneous behavior of electrons and holes with profound consequences on optical properties.
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…
Recently, longitudinal acoustic phonons have been identified as the main source of the intensity damping observed in Rabi rotation measurements of the ground-state exciton of a single InAs/GaAs quantum dot. Here we report experiments of intensity damped Rabi rotations in the case of detuned laser pulses, the results have implications for the coherent optical control of both excitons and spins using detuned laser pulses.
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…
We study experimentally the dependence of dynamic nuclear spin polarization on the power of non-resonant optical excitation in two types of individual neutral semiconductor quantum dots: InGaAs/GaAs and GaAs/AlGaAs. We show that the mechanism of nuclear spin pumping via second order recombination of optically forbidden (''dark'') exciton states recently reported in InP/GaInP quantum dots [Phys. Rev. B 83, 125318 (2011)] is relevant for material systems considered in this work. In the InGaAs/GaAs dots this nuclear spin polarization mechanism is particularly pronounced, resulting in Overhauser s…
The carrier spin dynamics in a n-doped (In,Ga)As/GaAs quantum well has been studied by time-resolved Faraday rotation and ellipticity techniques in the temperature range down to 430 milliKelvin. These techniques give data with very different spectral dependencies, from which nonetheless consistent information on the spin dynamics can be obtained, in agreement with theoretical predictions. The mechanisms of long-lived spin coherence generation are discussed for the cases of trion and exciton resonant excitation. We demonstrate that carrier localization leads to a saturation of spin relaxation t…
Elimination of the acoustoelectric domain and increasing of the emission intensity by means of shunting the lateral current in the InGaAs/GaAs heterostructures
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…
In this work, we present and evaluate a (111)-rotated eight-band $\mathbf{k}\cdot\mathbf{p}$ Hamiltonian for the zinc-blende crystal lattice to investigate the electronic properties of site-controlled InGaAs/GaAs quantum dots grown along the [111] direction. We derive the rotated Hamiltonian including strain and piezoelectric potentials. In combination with our previously formulated (111)-oriented continuum elasticity model, we employ this approach to investigate the electronic properties of a realistic site-controlled (111)-grown InGaAs quantum dot. We combine these studies with an evaluation…
We report experimental evidence identifying acoustic phonons as the principal source of the excitation-induced-dephasing (EID) responsible for the intensity damping of quantum dot excitonic Rabi rotations. The rate of EID is extracted from temperature dependent Rabi rotation measurements of the ground-state excitonic transition, and is found to be in close quantitative agreement with an acoustic-phonon model.
In this Letter, four-point magnetotransport of high mobility InGaAs/InP heterointerfaces is measured from 1.6 K to 300 K and from 0 to 15 T, and an analysis is shown whereby the mobility and density of the two-dimensional (2D) accumulation layer can be separately characterized from that of the parallel conducting dopant layer over all but a small intermediate temperature range. Standard magnetotransport regimes are defined as the temperature increases from 1.6 K to 300 K, namely quantum Hall (QH), Shubnikov de Haas (SdH), and Drude regimes (D), and in the QH and D regimes different analyses ar…
We present a study on the influence of strain-relieving InAlAs buffer layers on metamorphic InAs/InGaAs quantum wells grown by molecular beam epitaxy on GaAs. Residual strain in the buffer layer, the InGaAs barrier and the InAs wells were assessed by X-ray diffraction and high-resolution transmission electron microscopy. By carefully choosing the composition profile and thicknesses of the buffer layer, virtually unstrained InGaAs barriers embedding an InAs quantum well with thickness up to 7nm can be grown. This allows reaching low-temperature electron mobilities much higher than previously re…
The resistivity (R) of low mobility dilute 2D-electron gas in a n-InGaAs/GaAs double quantum well (DQW) exhibits the monotonic 'insulating-like' temperature dependence (dR/dT < 0) at T = 1.8 -- 70K in zero magnetic field. This temperature interval corresponds to a ballistic regime (kTtau/hbar > 0.1 -- 3.5) for our samples, and the electron density is on a 'insulating' side of the so-called B = 0 2D metal--insulator transition. We show that the observed localization and Landau quantization is due to the Sigma_xy(T)anomalous T-dependence.
The current-induced spin polarization and momentum-dependent spin-orbit field were measured in In$_{x}$Ga$_{1-x}$As epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin polarization mechanism must be considered. Theoretical calculatio…
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 $\mathbf{k}\cdot\math…
AlGaAs nanowires as a universal platform for GaAs, InGaAs, and InAs quantum dots
Technical University of Denmark（丹麦技术大学）；St. Petersburg State University（圣彼得堡国立大学）；Université Paris Saclay（巴黎萨克雷大学）；CNRS（法国国家科学研究中心）；Alferov University（阿尔费罗夫大学）
Characteristics of GaAs/In$_{x}$Ga$_{1-x}$As/GaAs heterostructures with a single quantum well, which were obtained at various growth parameters, are evaluated according to the results of measurements of low-temperature photoluminescence spectra and their corresponding theoretical analysis.
We present here the electronic structure and optical properties of InGaAs quantum wells with barrier doped with Manganese. We calculated the electronic states and optical emission within the envelope function and effective mass approximations using the spin-density functional theory in the presence of an external magnetic field. We observe magneto-oscillations of the Landau levels at low-magnetic fields (B < 5 T) that are dominated by the magnetic interaction between holes spin and Mn spin, while at high magnetic fields the spin-polarization of the hole gas is the dominant effect. Our results …
This paper reports on the observation and analysis of magnetotransport phenomena in the nonlinear differential resistance $r_{xx}=dV_{xx}/dI$ of high-mobility InGaAs/InP and GaAs/AlGaAs Hall bar samples driven by direct current, $\Idc$. Specifically, it is observed that Shubnikov -de Haas (SdH) oscillations at large filling factors invert their phase at sufficiently large values of $\Idc$. This phase inversion is explained as being due to an electron heating effect. In the quantum Hall effect regime the $r_{xx}$ oscillations transform into diamond-shaped patterns with different slopes correspo…
In the avalanche regime we observed the negative photoconductance of heterostructures of silicon dioxide films containing cobalt nanoparticles grown on gallium arsenide, SiO2(Co)/GaAs. Light irradiation with the photon energy less than the bandgap energy of the GaAs creates holes trapped on defects within the GaAs bandgap, suppresses the avalanche feedback and causes a reduction of the current flowing in the SiO2(Co)/GaAs.
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…
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…
In this work, we have theoretically investigated the intermixing effect in highly strained In$_{0.3}$Ga$_{0.7}$As/GaAs quantum well (QW) taking into consideration the composition profile change resulting from in-situ indium surface segregation. To study the impact of the segregation effects on the postgrowth intermixing, one dimensional steady state Schrodinger equation and Fick's second law of diffusion have been numerically solved by using the finite difference methods. The impact of the In/Ga interdiffusion on the QW emission energy is considered for different In segregation coefficients. O…
The InAs/InGaAs DWELL solar cell grown by MBE is a standard pin diode structure with six layers of InAs QDs embedded in InGaAs quantum wells placed within a 200-nm intrinsic GaAs region. The GaAs control wafer consists of the same pin configuration but without the DWELL structure. The typical DWELL solar cell exhibits higher short current density while maintaining nearly the same open-circuit voltage for different scales, and the advantage of higher short current density is more obvious in the smaller cells. In contrast, the smaller size cells, which have a higher perimeter to area ratio, make…
InGaAs Quantum Dots embedded in GaAs barriers, grown in inverted tetrahedral recesses of 7 μm edge, have showed interesting characteristics in terms of uniformity and spectral narrowness of the emission. In this paper we present a study on the fine structure splitting (FSS). The investigation of about 40 single quantum dots revealed two main points: (1) the values of this parameter are very similar from dot to dot, proving again the uniformity of Pyramidal QD properties, (2) there is a little chance, in the sample investigated, to find a dot with natural zero splitting, but the values found (t…
We study the quantum critical behavior of the plateau-insulator (PI) transition in a low mobility InGaAs/InP heterostructure. By reversing the direction of the magnetic field (B) we find an averaged Hall resistance ρ_xy which remains quantized at the plateau value h/e^2 throughout the PI transition. We extract a critical exponent κ'= 0.57 +/- 0.02 for the PI transition which is slightly different from (and possibly more accurate than) the established value 0.42 +/- 0.04 as previously obtained from the plateau-plateau (PP) transitions.
We have studied the efficacy of (NH4)2Sx surface passivation on the (311)A GaAs surface. We report XPS studies of simultaneously-grown (311)A and (100) heterostructures showing that the (NH4)2Sx solution removes surface oxide and sulfidizes both surfaces. Passivation is often characterized using photoluminescence measurements, we show that while (NH4)2Sx treatment gives a 40 - 60 x increase in photoluminescence intensity for the (100) surface, an increase of only 2 - 3 x is obtained for the (311)A surface. A corresponding lack of reproducible improvement in the gate hysteresis of (311)A hetero…
We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse-areas of up to $14π$. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse-area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb-shift.
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…
Multiple quantum beats of a system of the coherently excited quantum confined exciton states in a high-quality heterostructure with a wide InGaAs/GaAs quantum well are experimentally detected by the spectrally resolved pump-probe method for the first time. The beat signal is observed as at positive as at negative delays between the pump and probe pulses. A theoretical model is developed, which allows one to attribute the QBs at negative delay to the four-wave mixing (FWM) signal detected at the non-standard direction. The beat signal is strongly enhanced by the interference of the FWM wave wit…
We probe the electron transport properties in the shell of GaAs/In0.2Ga0.8As core/shell nanowires at high electric fields using optical pump / THz probe spectroscopy with broadband THz pulses and peak electric fields up to 0.6 MV/cm. The plasmon resonance of the photoexcited charge carriers exhibits a systematic redshift and a suppression of its spectral weight for THz driving fields exceeding 0.4 MV/cm. This behavior is attributed to the intervalley electron scattering resulting in the increase of the average electron effective mass and the corresponding decrease of the electron mobility by a…
We demonstrate a scheme for optically patterning nuclear spin polarization in semiconductor/ferromagnet heterostructures. A scanning time-resolved Kerr rotation microscope is used to image the nuclear spin polarization that results when GaAs/MnAs epilayers are illuminated with a focused laser having a Gaussian profile. Rather than tracking the intensity profile of the laser spot, these images reveal that the nuclear polarization forms an annular lateral structure having circular symmetry with a dip rather than a peak at its center.
The effect of irradiation by 30-keV Ga+ and 35-keV He+ ions (in relatively small doses) on the excitonic reflectivity spectra of single InGaAs/GaAs quantum-well structures is studied. It is found that the irradiation results in decreasing intensity and broadening of the excitonic resonances in the reflectivity spectra for all the doses. It is shown that these changes are not related to a decrease of the exciton transition oscillator strength and, therefore, to the irradiation-induced destruction of the excitonic states, but can be rather ascribed to a common cause, namely, to inhomogeneous bro…
Gate instability/hysteresis in modulation-doped p-type AlGaAs/GaAs heterostructures impedes the development of nanoscale hole devices, which are of interest for topics from quantum computing to novel spin physics. We present an extended study conducted using custom-grown, matched modulation-doped n-type and p-type heterostructures, with/without insulated gates, aimed at understanding the origin of the hysteresis. We show the hysteresis is not due to the inherent `leakiness' of gates on p-type heterostructures, as commonly believed. Instead, hysteresis arises from a combination of GaAs surface-…
Monolithic axial InGaAs quantum dot emitters in GaAs-based nanowires via Sb-mediated facet engineering
Walter Schottky Institute, TUM School of Natural Sciences, Technical University of Munich（慕尼黑工业大学沃尔特·施科特基研究所自然科学学院）；Institute for Physics and Astronomy, Technical University Berlin（柏林工业大学物理与天文学研究所）；Department of Chemistry, Ludwig-Maximilians-University of Munich（慕尼黑大学化学系）；Walter Schottky Institute, TUM School of Computation, Information and Technology, Technical University of Munich（慕尼黑工业大学沃尔特·施科特基研究所计算、信息与技术学院）；Department of Physics, University of California, Berkeley（加州大学伯克利分校物理系）
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…
Exponentially small resistance in crossed static magnetic and microwave fields occurs in ultrapure two dimensional electron gases (2DEG), while in less pure systems the magnetoresistance oscillates but is always positive. A non-perturbative theory of self-organization explains the new collective states in terms of open orbits. There are analogies to many other anomalous physical phenomena, as well as to scaling and evolutionary principles of biophysics.
A detailed theoretical study of the optical absorption in self-assembled quantum dots is presented in this paper. A rigorous atomistic strain model as well as a sophisticated electronic band structure model are used to ensure accurate prediction of the optical transitions in these devices . The optimized models presented in this paper are able to reproduce the experimental results with an error less than 1$\%$. The effects of incident light polarization, alloy mole fraction, quantum dot dimensions, and doping have been investigated. The in-plane polarized light absorption is more significant t…
We report on a process that enables the removal of II-VI semiconductor epilayers from their GaAs growth substrate and their subsequent transfer to arbitrary host environments. The technique combines mechanical lapping and layer selective chemical wet etching and is generally applicable to any II-VI layer stack. We demonstrate the non-invasiveness of the method by transferring an all-II-VI magnetic resonant tunneling diode. High resolution X-ray diffraction proves that the crystal integrity of the heterostructure is preserved. Transport characterization confirms that the functionality of the de…
We present results of atomistic empirical pseudopotential calculations and configuration interaction for excitons, positive and negative trions (X\pm), positive and negative quartons (X2\pm) and biexcitons. The structure investigated are laterally aligned InGaAs quantum dot molecules embedded in GaAs under a lateral electric field. The rather simple energetic of excitons becomes more complex in the case of charged quasiparticles but remains tractable. The negative trion spectrum shows four anticrossings in the presently available range of fields while the positive trion shows two. The magnitud…
We have measured weak antilocalization effects, universal conductance fluctuations, and Aharonov-Bohm oscillations in the two-dimensional electron gas formed in InGaAs/AlInAs heterostructures. This system possesses strong spin-orbit coupling and a high Landé factor. Phase-coherence lengths of 2$-$4 $μ$m at 1.5$-$4.2 K are extracted from the magnetoconductance measurements. The analysis of the coherence-sensitive data reveals that the temperature dependence of the decoherence rate complies with the dephasing mechanism originating from electron-electron interactions in all three experiments. Dis…
We implement metallic layers of Si-doped (110) GaAs as modulation doping in high mobility p-type heterostructures, changing to p-growth conditions for the doping layer alone. The strongly auto-compensated doping is first characterized in bulk samples, identifying the metal-insulator transition density and confirming classic hopping conduction in the insulating regime. To overcome the poor morphology inherent to Si p-type (110) growth, heterostructures are fabricated with only the modulation doping layer grown under p-type conditions. Such heterostructures show a hole mobility of 1.75x10^2 cm^2…
Self-selective growth of GaAs1-xBix on GaAs zinc blende/wurtzite nanowire heterostructures
Lund University（隆德大学）；NanoLund, Lund University（隆德大学纳米隆德）；Centre for Analysis and Synthesis, Lund University（隆德大学分析与合成中心）；MAX IV Laboratory, Lund University（隆德大学MAX IV实验室）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯玻尔研究所）
The disordered potential landscape in an InGaAs/InAlAs two-dimensional electron gas patterned into narrow wires is investigated by means of scanning gate microscopy. It is found that scanning a negatively charged tip above particular sites of the wires produces conductance oscillations that are periodic in the tip voltage. These oscillations take the shape of concentric circles whose number and diameter increase for more negative tip voltages until full depletion occurs in the probed region. These observations cannot be explained by charging events in material traps, but are consistent with Co…
We report an experimental study of quantum conductivity corrections for two-dimensional electron gas in a GaAs/InGaAs/GaAs single and double quantum wells in a wide temperature range (1.8-100) K. We perform a comparison of our experimental data for the longitudinal conductivity at zero magnetic field to the theory of interaction-induced corrections to th transport coefficients. In the temperature range from 10 K up to (45-60) K, wich covers the ballistic interaction regimes for our samples, a rather good agreement between the theory and our experimental results has been found.
The electron-electron interaction quantum correction to the conductivity of the gated double well Al$_x$Ga$_{1-x}$As/GaAs structures is investigated experimentally. The analysis of the temperature and magnetic field dependences of the conductivity tensor allows us to obtain reliably the diffusion part of the interaction correction for the regimes when the structure is balanced and when only one quantum well is occupied. The surprising result is that the interaction correction does not reveal resonant behavior; it is practically the same for both regimes.
Quantum devices formed in high-electron-mobility semiconductor heterostructures provide a route through which quantum mechanical effects can be exploited on length scales accessible to lithography and integrated electronics. The electrostatic definition of quantum dots in semiconductor heterostructure devices intrinsically involves the lithographic fabrication of intricate patterns of metallic electrodes. The formation of metal/semiconductor interfaces, growth processes associated with polycrystalline metallic layers, and differential thermal expansion produce elastic distortion in the active …
