共查询到20条相似文献,搜索用时 625 毫秒
1.
D. Bougeard K. Brunner G. Abstreiter 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):609
In this contribution we study the intravalence band photoexcitation of holes from self-assembled Ge quantum dots (QDs) in Si followed by spatial carrier transfer into SiGe quantum well (QW) channels located close to the Ge dot layers. The structures show maximum response in the important wavelength range 3–5 μm. The influence of the SiGe hole channel on photo- and dark current is studied depending on temperature and the spatial separation of QWs and dot layers. Introduction of the SiGe channel in the active region of the structure increases the photoresponsivity by up to about two orders of magnitude to values of 90 mA/W at T=20 K. The highest response values are obtained for structures with small layer separation (10 nm) that enable efficient transfer of photoexcited holes from QD to QW layers. The results indicate that Si/Ge QD structures with lateral photodetection promise very sensitive large area mid-infrared photodetectors with integrated readout microelectronics in Si technology. 相似文献
2.
S. N. Molotkov 《JETP Letters》1996,64(3):237-243
A realization of a quantum controlled-NOT gate based on a single quantum dot is proposed.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 219–224 (10 August 1996) 相似文献
3.
I. Ţifrea M. Crisan I. Grosu 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):455-464
We consider the transport and the noise characteristic in the case of a triple quantum dots T-shape system where two of the
dots form a two-level system and the other works in a detector-like setup. Our theoretical results are obtained using the
equation of motion method for the case of zero and finite on-site Coulomb interaction in the detector dot. We present analytic
results for the electronic Green’s functions in the system’s component quantum dots, and we used numerical calculations to
evaluate the system’s transport properties. The transport trough the T-shaped system can be controlled by varying the coupling
between the two-level system dots or the coupling between the detector dot and the exterior electrodes. The system’s conductance
presents Fano dips for both strong (fast detector) and weak coupling (slow detector) between the detector dot and the external
electrodes. Due to stronger electronic correlations the noise characteristics in the case of a slow detector are much higher.
This setup may be of interest for the practical realization of qubit states in quantum dots systems. 相似文献
4.
M. J. Ma M. B. A. Jalil S. G. Tan D. E. Koh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,82(1):37-46
We theoretically study the spin-polarized transport
through double barrier magnetic tunnel junction (DBMTJ) consisting
of the quantum dot sandwiched by two ferromagnetic (FM) leads. The
tunneling current through the DBMTJ is evaluated based on the
Keldysh nonequilibrium Green’s function approach. The self-energy
and Green’s function of the dot are analytically obtained via the
equation of motion method, by systematically incorporating two
spin-flip phenomena, namely, intra-dot spin-flip, and spin-flip
coupling between the lead and the central dot region. The effects of
both spin-flip processes on the spectral functions, tunneling
current and tunnel magnetoresistance (TMR) are analyzed. The
spin-flip effects result in spin mixing, thus contributing to the
spectral function of the off-diagonal Green’s function components ( Gs[`(s)] r )\left( {G_{\sigma \bar \sigma }^r } \right). Interestingly, the spin-flip coupling
between the lead and dot enhances both the tunneling current and the
TMR for applied bias above the threshold voltage V
th
. On the
other hand, the intra-dot spin-flip results in an additional step in
the I-V characteristics near V
th
. Additionally, it
suppresses the tunneling current but enhances the TMR. The opposing
effects of the two types of spin-flip on the tunneling current means
that one spin-flip mechanism can be engineered to counteract the
other, so as to maintain the tunneling current without reducing the
TMR. Their additive effect on the TMR enables the DBMTJ to attain a
large tunneling current and high TMR for above threshold bias
values. 相似文献
5.
S. M. Amirkhanyan E. M. Kazaryan H. A. Sarkisyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2014,49(6):264-271
Current of the spin magnetic moment of an electron coupled with hydrogen-like impurity, placed in the center of a spherical quantum dot, is studied. Confinement potential of the quantum dot is approximated by rectangular infinitely high walls. S-states of electron for both positive and negative values of total energy are considered. Dependences of spin magnetic moment current of electron on the radial variable for different values of dot radius are obtained. It is shown that for quantum dots with large radius, due to weakening of size-quantization effect, corresponding curves approach each other. 相似文献
6.
This paper investigates theoretically the electronic structure and
transport of a two-level quantum dot irradiated under a strong laser
field at low temperatures. Using the method of Keldysh equation of
motion for nonequilibrium Green functions, it examines the
time-averaged density of states and conductance for the system with
photon polarization parallel with and perpendicular to the tunnelling
current direction respectively. It is demonstrated that, by analysing
some numerical examples, more photon sidebands resonance states and
multi- and single-photon transitions are found when diagonal matrix
elements dominate the interaction, while the electronic transitions
due to multiphoton absorption are more or less suppressed when
off-diagonal interaction dominates. 相似文献
7.
We present a variational calculation for the ground state of the double donor in a spherical GaAs–Ga1–x
Al
x
As quantum dot. The binding energies for the ionized and neutral centres are calculated for several barrier height values as a function of the radius of the dot. Compared with a square well structure, there is a stronger confinement and a larger binding energy for the double donors in a spherical quantum dot. 相似文献
8.
The time-dependent electron transport through a quantum dot with the additional over-dot (bridge) tunneling channel within the evolution operator technique has been studied. The microwave field applied to the leads and quantum dot has been considered and influence of the time-dependent shift of corresponding energy levels on the quantum dot charge and current flowing in the system, its time-averaged values and derivatives of the average current with respect to the gate and source–drain bias voltages have been investigated. The influence of the over-dot tunneling channel on the photon-assisted tunneling has been also studied. 相似文献
9.
C. Jiang X. F. Xie W. J. Gong G. Z. Wei 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(2):237-245
Nonequilibrium electron and spin transport properties in a
parallel double quantum dot (QD) Fano interferometer are
theoretically studied. With the shift of gate voltage around the
chemical potential of either lead, we find the Fano lineshapes in
the differential conductance spectra, which is sensitively
determined by the bias voltage strength and appropriate QD level
distributions. The intradot Coulomb interactions modulate the Fano
interference in a substantial way and can induce the emergence of
negative differential conductance, because of its nontrivial role in
splitting the QD levels. In the presence of a local Rashba
spin-orbit coupling, the interplay between the magnetic and Rashba
fields induces the occurrence of the nonequilibrium spin-related
Fano interference, different from the linear-transport results.
Furthermore, the striking Coulomb-driven spin accumulation in the
‘resonant-channel’ QD appears. 相似文献
10.
S. Shojaei 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(2):197-201
The present work investigates the nonlinear optical properties of a GaN quantum dot in the disk limit via the exciton and
biexciton states using the compact density matrix formalism. Based on this model, we calculate the ground state energy of
the exciton and biexciton states by the variation method, within envelope function and effective mass approximations. Linear
and nonlinear optical absorption (α
(1), α
(3)) and oscillator strengths attributed to the optical transitions are obtained. The details of the behaviour of α
(1) and α
(3) around the resonance frequencies and for different quantum dot geometries are presented. It is found that the size of quantum
dot and the optical intensity have a remarkable effect on the optical absorption, and the biexcitonic two-photon absorption
coefficient(K
2) has also been calculated in this system. The results show that this parameter is strongly affected by the size of the quantum
dot. 相似文献
11.
We investigate mesoscopic transport through a system that consists of a central quantum dot (QD) and two single-wall
carbon nanotube (SWCN) leads in the presence of a rotating
magnetic field. The spin-flip effect is induced by the rotating
magnetic field, and the tunnelling current is sensitively related
to the spin-flip effect. We present the calculations of charge
and spin current components to show the intimate relations to the
SWCN leads. Zeeman effect is important when the applied magnetic
field is strong enough. The current characteristics are quite
different when the source-drain bias is zero (eV=0) and nonzero
(eV≠0). The asymmetric peak and valley of spin current versus
gate voltage exhibit Fano resonance. Multi-resonant peaks of spin
current versus photon energy ħω reflect the structure
of CN quantum wires, as well as the resonant photon absorption and
emission effect. The matching-mismatching of channels in the CN
leads and QD results in novel spin current structure by tuning the
frequency. 相似文献
12.
M. Sopanen H. Lipsanen J. Tulkki J. Ahopelto 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
Coupled double quantum dots and quantum dot superlattices are formed by utilizing the strain of an InP island on top of a near-surface multi-quantum-well structure. The number and composition of the quantum wells together with the thickness of the barrier separating the quantum wells are varied to investigate the coupling of the wave functions of the carriers confined in separate vertically stacked dots. Photoluminescence studies show that the reduction of the barrier thickness and the increase of the number of wells enhance the coupling, which is observed as red shift and narrowing of the quantum dot peak. The calculated shifts of the peak positions agree closely with the experimental values. 相似文献
13.
A. K. Atayan E. M. Kazaryan A. V. Meliksetyan H. A. Sarkisyan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):485-492
The absorption of light in an ensemble of non-interacting cylindrical quantum dots in the presence of a magnetic field is
discussed using a model consisting of dots with rectangular infinitely-high potential barriers. The ensemble’s absorption
coefficient is calculated — as well as the threshold frequency of absorption — as a function of the applied magnetic field
and the quantum dot size. Theoretical results are compared with experimental data on magneto-luminescence in an In0.53Ga0.47As/InP cylindrical quantum dot system. In addition, using a perturbation theory framework, the influence of excitonic effects
on the behaviour of the electron-hole energetic spectrum of said system is discussed. 相似文献
14.
15.
We exhibit the supersymmetric quantum mechanical structure of the full 3+1 dimensional Dirac equation considering ‘mass’ as
a function of coordinates. Its usefulness in solving potential problems is discussed with specific examples. We also discuss
the ‘physical’ significance of the supersymmetric states in this formalism. 相似文献
16.
We discuss questions pertaining to the definition of ‘momentum’, ‘momentum space’, ‘phase space’ and ‘Wigner distributions’;
for finite dimensional quantum systems. For such systems, where traditional concepts of ‘momenta’ established for continuum
situations offer little help, we propose a physically reasonable and mathematically tangible definition and use it for the
purpose of setting up Wigner distributions in a purely algebraic manner. It is found that the point of view adopted here is
limited to odd dimensional systems only. The mathematical reasons which force this situation are examined in detail 相似文献
17.
结合垂直腔面发射激光器(VCSEL)原理以及量子点增益特点,计算了有源层p掺杂结构的量子点VCSEL的材料增益和3 dB带宽,发现p掺杂结构可以大大提高频率特性.结合VCSEL激射条件和阈值特性,分析了对VCSEL结构的要求;分析了分布参数对频率特性的影响,对其外部封装提出了要求.设计了高频率响应的含氧化限制层的1.3 μm量子点VCSEL结构.
关键词:
量子点
垂直腔面发射激光器
微分增益
3 dB带宽 相似文献
18.
A recently developed unified theory of classical and quantum chaos, based on the de Broglie-Bohm (Hamilton-Jacobi) formulation
of quantum mechanics is presented and its consequences are discussed. The quantum dynamics is rigorously defined to be chaotic
if the Lyapunov number, associated with the quantum trajectories in de Broglie-Bohm phase space, is positive definite. This
definition of quantum chaos which under classical conditions goes over to the well-known definition of classical chaos in
terms of positivity of Lyapunov numbers, provides a rigorous unified definition of chaos on the same footing for both the
dynamics. A demonstration of the existence of positive Lyapunov numbers in a simple quantum system is given analytically,
proving the existence of quantum chaos. Breaking of the time-reversal symmetry in the corresponding quantum dynamics under
chaotic evolution is demonstrated. It is shown that the rigorous deterministic quantum chaos provides an intrinsic mechanism
towards irreversibility of the Schrodinger evolution of the wave function, without invoking ‘wave function collapse’ or ‘measurements’ 相似文献
19.
Quantum dot infrared photodetectors (QDIPs) are more efficient than other types of semiconductor based photodetectors; so it has become an actively developed field of research. In this paper quantum dot infrared photodetector dark current is evaluated theoretically. This evaluation is based on the model that was developed by Ryzhii et al. Here it is assumed that both thermionic emission and field-assisted tunneling mechanisms determine the dark current of QDIPs; moreover we have considered Richardson effect, which has not been taken into account in previous research. Then a new formula for estimating average number of electrons in a quantum dot infrared photodetector is derived. Considering the Richardson effect and field-assisted tunneling mechanisms in the dark current improves the accuracy of algorithm and causes the theoretical data to fit better in the experiment. The QDIPs dark current temperature and biasing voltage dependency, contribution of thermionic emission and field-assisted tunneling at various temperatures and biasing voltage in the QDIPs dark current are investigated. Moreover, the other parameter effects like quantum dot (QD) density and QD size effect on the QDIPs dark current are investigated. 相似文献
20.
L. P. Kouwenhoven A. T. Johnson N. C. van der Vaart A. van der Enden C. J. P. M. Harmans C. T. Foxon 《Zeitschrift für Physik B Condensed Matter》1991,85(3):381-388
We have performed RF experiments on a lateral quantum dot defined in the two dimensional electron gas (2DEG) of a GaAs/AlGaAs heterostructure. The small capacitance of the quantum dot gives rise to single-electron charging effects, which we employed to realize a quantum dot turnstile device. By modulating the tunnel barriers between the quantum dot and the 2DEG leads with two phase-shifted RF signals, we pass an integer number of electrons through the quantum dot per RF cycle. This is demonstrated by the observation of quantized current plateaus at multiples ofef in current-voltage characteristics, wheref is the frequency of the RF signals. When an asymmetry is induced by applying unequal RF voltages, our quantum dot turnstile operates as a single-electron pump producing a quantized current at zero bias voltage. 相似文献