共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Offermans P.M. Koenraad J.H. Wolter D. Granados J.M. García V.M. Fomin V.N. Gladilin J.T. Devreese 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):41
We present an atomic-scale analysis of the indium distribution of self-assembled (In,Ga)As quantum rings (QRs), which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20 nm, which is consistent with the observed electronic radius of QR structures. Based on the structural information from the X-STM measurements, we calculate the magnetization as a function of the applied magnetic field. We conclude that, although the real QR shape differs strongly from an idealized circular-symmetric open ring structure, Aharonov–Bohm-type oscillations in the magnetization can be expected. 相似文献
2.
J. Gomis J. Martínez-Pastor B. Alén D. Granados J. M. García P. Roussignol 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):471-477
We present a study of the primary optical transitions
and recombination dynamics in InGaAs self-assembled quantum
nanostructures with different shape. Starting from the same
quantum dot seeding layer, and depending on the overgrowth
conditions, these new nanostructures can be tailored in shape and
are characterized by heights lower than 2 nm and base lengths
around 100 nm. The geometrical shape strongly influences the
electronic and optical properties of these nanostructuctures. We
measure for them ground state optical transitions in the range
1.25–1.35 eV and varying energy splitting between their excited
states. The temperature dependence of the exciton recombination
dynamics is reported focusing on the intermediate temperature
regime (before thermal escape begins to be important). In this
range, an important increase of the effective photoluminescence
decay time is observed and attributed to the state filling and
exciton thermalization between excited and ground states. A rate
equation model is also developed reproducing quite well the
observed exciton dynamics. 相似文献
3.
We analyze the effect of the spatial correlation on the ground state energy of two particles (two electrons and exciton–hole pair) confined in quantum ring (QR) with a soft-edge-barrier confinement potential. Starting from the Schrödinger variational principle we derive a one-dimensional differential equation for the spatial pair correlation function (SPCF), which we solve numerically by using the shooting method. The effect of the repulsive core in a self-assembled GaAs/InAs QR on the two-electron and exciton SPCF is analyzed. A comparative analysis of the dependencies of the two-particle ground state energies on the inner and outer radii of GaAs/InAs QRs with different confinement potential shapes is presented. 相似文献
4.
J. Planelles J.I. Climente F. Rajadell 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):370-375
The electronic states of semiconductor quantum rings (QRs) under tilted magnetic fields are studied in the framework of the effective mass and envelope function approximations. For an axial field, the orbital Zeeman contribution prevails leading to the well-known Aharanov–Bohm spectrum, but it slowly decreases as the magnetic field direction declines. For an in-plane field, only the diamagnetic shift survives and it leads to the formation of double quantum well solutions, this result being relevant for experimental techniques which use in-plane magnetic fields to determine the spin of QR ground states. We also investigate the magnetic response of partially overlapped QRs, which are characteristic of high-density samples of self-assembled rings, and find that the spectrum is quite sensitive to ring coupling. 相似文献
5.
本文报道了采用分子束外延技术制备的三色InAs/GaAs量子点红外探测器. 器件采用nin型结构, 吸收区结构是在InGaAs量子阱中生长含有AlGaAs插入层的InAs量子点, 器件在77 K下的红外光电流谱有三个峰值: 6.3, 10.2和11 μm. 文中分析了它们的跃迁机制, 并且分别进行了指认. 因为有源区采用了不对称结构, 所以器件在外加偏压正负方向不同时, 光电流谱峰值的强度存在一些差异. 不论在正偏压或者负偏压下, 当偏压达到较高值, 再进一步增大偏压时, 都出现了对应于连续态的跃迁峰强度明显下降的现象, 这是由量子点基态与阱外连续态的波函数交叠随着偏压进一步增大而迅速减小导致的. 相似文献
6.
V. V. Danilov A. V. Baranov G. K. El’yashevich A. O. Orlova G. G. Khokhlov A. I. Khrebtov 《Optics and Spectroscopy》2010,108(6):941-946
The fluorescence of CdSe/ZnS semiconductor quantum rods (QRs) in the CdSe/ZnS-hexane pentylcyanobiphenyl and CdSe/ZnS-methyl
methacrylate pentylcyanobiphenyl multicomponent systems has been investigated. It is shown that the presence of pentylcyanobiphenyl
affects differently the QR fluorescence in each composite. The QR fluorescence in hexane solutions is efficiently quenched
in the presence of pentylcyanobiphenyl, whereas in the composites based on methyl-methacrylate the QR fluorescence is enhanced
as a result of the introduction of pentylcyanobiphenyl in the mesomorphic state. This difference is explained by the different
forms of pentylcyanobiphenyl in these systems. The composites based on structured porous polyethylene films containing QRs
in a mesomorphic medium have been obtained for the first time. The measured degree of polarization of the QR fluorescence
characterizes the composite as strongly ordered. 相似文献
7.
R. Timm J. Grabowski H. Eisele A. Lenz S.K. Becker L. Müller-Kirsch K. Ptschke U.W. Pohl D. Bimberg M. Dhne 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):231
GaSb nanostructures in GaAs, grown by metalorganic chemical vapor deposition, were studied with cross-sectional scanning tunneling microscopy. Three different samples were examined, containing a thin quantum well, a quantum well near the critical thickness for dot formation, and finally self-organized quantum dots with base lengths of 5–8 nm and heights of about 2 nm. The dots are intermixed with a GaSb content between 60% and 100%. Also small 3D and 2D islands were observed, possibly representing quantum dots in an early growth stage and quantum dot precursors. All GaSb layers exhibit gaps, which are indications of an island-like growth mode during epitaxy. 相似文献
8.
A particular subject of investigation is the role of several sadle-point contact (QPC) parameters on the scattering properties of an Aharonov–Bohm–Aharonov–Casher quantum ring (QR) under Rashba-type spin orbit interaction. We discuss the interplay of the conductance with the confinement strengths and height of the QPC, which yields new and tunable harmonic and non-harmonics patterns, while one manipulates these constriction parameters. This phenomenology may be of utility to implement a novel way to modulate spin interference effects in semiconducting QRs, providing an appealing test-platform for spintronics applications. 相似文献
9.
We show how the atomistic pseudopotential many-body theory of InGaAs/GaAs addresses some important effects, including (i) the fine-structure splittings (originating from interband spin exchange), (ii) the optical spectra of charged quantum dots and (iii) the degree of entanglement in a quantum dot molecule. 相似文献
10.
M.L. Vallejo 《Physics letters. A》2010,374(48):4928-4932
We propose an efficient spin-filter device by exploiting bound states (BICs) in the continuum and Fano effect on a triple Rashba quantum dot molecule embedded in an Aharonov-Bohm interferometer. We find that the coexistence of a BIC and a Fano antiresonance result in polarizations close to 100% in wide regions in the space of parameters. 相似文献
11.
In this study, a detailed investigation of the size effects of an exciton–acceptor complex in a disc-like quantum dot has been carried out by using the matrix diagonalization method and the compact density-matrix approach. We calculate the binding energy and the oscillator strength of intersubband quantum transition from the ground state into the first excited state as a function of the dot radius. Based on the computed energies and wave functions, the linear, third-order and total optical absorption coefficients as well as the refractive index have been examined between the ground and the first excited states. We find that the all absorption spectra and refractive index changes are strongly affected by the quantum dot size. However, for two cases of a smaller dot and a larger dot, the results of quantum size effects on the optical absorptions are opposite. 相似文献
12.
This paper reports on the use of a local order measure to quantify the spatial ordering of a quantum dot array (QDA). By means of electron ground state energy analysis in a quantum dot pair, it is demonstrated that the length scale required for such a measure to characterize the opto-electronic properties of a QDA is of the order of a few QD radii. Therefore, as local order is the primary factor that affects the opto-electronic properties of an array of quantum dots of homogeneous size, this order was quantified through using the standard deviation of the nearest neighbor distances of the quantum dot ensemble. The local order measure is successfully applied to quantify spatial order in a range of experimentally synthesized and numerically generated arrays of nanoparticles. This measure is not limited to QDAs and has wide ranging applications in characterizing order in dense arrays of nanostructures. 相似文献
13.
F.M. Gmez-Campos S. Rodríguez-Bolívar C.M. de Jong van Coevorden A. Luque-Rodríguez P. Lara-Bullejos J.E. Carceller 《Physica E: Low-dimensional Systems and Nanostructures》2009,41(9):1712-1717
In this work we present a fast and accurate genetic algorithm to determine the envelope functions and eigenenergies of the ground states of electrons and holes in low-dimensional complex semiconductor structures. We have developed the theoretical formalism of the algorithm in a general way in order to make it easy to include arbitrary nonparabolic and anisotropic band profiles in the calculations. From these results, calculation of the bandgaps of nanostructures can be carried out efficiently.Besides presenting and testing the algorithm, we calculate the ground state of electron and holes in two-dimensional quantum dot arrays, taking nonparabolicity and anisotropy into account. 相似文献
14.
Kinetic Monte Carlo simulations of optimization of self-assembly quantum rings growth strategy based on substrate engineering
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In this paper, the kinetic Monte Carlo simulations of the self-assembly quantum rings (QRs) based on the substrate engineering, which is related to the eventual shape of the formed quantum ring, are implemented. According to the simulation results, the availability of the QR with tunable size and the formation of smooth shape on the ideal flat substrate are checked. Through designing the substrate engineering, i.e., changing the depth, the separation and the ratio between the radius and the height of the embedded inclusions, the position and size of QR can be controlled and eventually the growth strategy of optimizing the self-assembly QRs is accomplished. 相似文献
15.
Wenfang Xie 《Physica B: Condensed Matter》2012,407(7):1134-1138
Using the matrix diagonalization method and the compact density-matrix approach, we studied the combined effects of hydrostatic pressure and temperature on the electronic and optical properties of an exciton-donor complex in a disc-shaped quantum dot. We have calculated the binding energy and the oscillator strength of the intersubband transition from the ground state into the first excited state as a function of the dot radius. Based on the computed energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients as well as the refractive index have been examined. We find that the ground state binding energy and the oscillator strength are strongly affected by the quantum dot radius, hydrostatic pressure and temperature. The results also show that the linear, third-order nonlinear and total absorption coefficients and refractive index changes strongly depend on temperature and hydrostatic pressure. 相似文献
16.
Zheng-Wei ZuoHong-Jing Xie 《Physics letters. A》2011,375(19):2007-2016
Under the dielectric continuum model and separation of variables, the interface optical (IO) phonon modes and electron-optical-phonon interaction in rectangular quantum wire and quantum dot embedded in a nonpolar matrix are studied. We found that there exist various types of IO phonon modes in rectangular nanostructures. The IO phonon modes in rectangular quantum wire include IO-propagating (IO-PR) and IO-IO hybrid phonon modes, while the IO phonon modes in rectangular quantum dot contain IO-IO-PR and IO-PR-PR hybrid phonon modes. The results of numerical calculation show that these hybrid phonon modes contain corner optical (CO) phonon modes and edge optical (EO) phonon modes. The potential applications of these results are also discussed. 相似文献
17.
Mohamed S. El-Tokhy Imbaby I. Mahmoud Hussein A. Konber 《Optical and Quantum Electronics》2009,41(11-13):933-956
This paper presents a theoretical analysis for the dark current characteristics of different quantum infrared photodetectors. These quantum photodetectors are quantum dot infrared photodetectors (QDIP), quantum wire infrared photodetectors (QRIP), and quantum well infrared photodetectors (QWIP). Mathematical models describing these devices are introduced. The developed models accounts for the self-consistent potential distribution. These models are taking the effect of donor charges on the spatial distribution of the electric potential in the active region. The developed model is used to investigate the behavior of dark current with different values of performance parameters such as applied voltage, number of quantum wire (QR) layers, QD layers, lateral characteristic size, doping quantum wire density and temperature. It explains strong sensitivity of dark current to the density of QDs/QRs and the doping level of the active region. In order to confirm our models and their validity on the practical applications, a comparison between the results obtained by proposed models and that experimentally published are conducted and full agreement is observed. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among them are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors. 相似文献
18.
M. Merano S. Sonderegger A. Crottini S. Collin E. Pelucchi P. Renucci A. Malko M.H. Baier E. Kapon J.D. Ganière B. Deveaud 《Applied physics. B, Lasers and optics》2006,84(1-2):343-350
An original time resolved cathodoluminescence set up has been used to investigate the optical properties and the carrier transport
in quantum structures located in InGaAs/AlGaAs tetrahedral pyramids. An InGaAs quantum dot formed just below the top of the
pyramid is connected to four types of low-dimensional barriers: InGaAs quantum wires on the edges of the pyramid, InGaAs quantum
wells on the (111)A facets and segregated AlGaAs vertical quantum wire and AlGaAs vertical quantum wells formed at the centre
and at the pyramid edges. Experiments were performed at a temperature of 92 K, an accelerating voltage of 10 kV and a beam
probe current of 10 pA. The cathodoluminescence spectrum shows five luminescence peaks. Rise and decay times for the different
emission wavelengths provide a clear confirmation of the peak attribution (previously done with other techniques) to the different
nanostructures grown in a pyramid. Moreover, experimental results suggest a scenario where carriers diffuse from the lateral
quantum structures towards the central structures (the InGaAs quantum dot and the segregated AlGaAs vertical quantum wire)
via the InGaAs quantum wires on the edges of the pyramid. According to this hypothesis, we have modeled the carrier diffusion
along these quantum wires. An ambipolar carrier mobility of 1400 cm2/V s allows to obtain a good fit to all temporal dependences.
PACS 78.67.-n 相似文献
19.
B. Solís 《Physics letters. A》2008,372(26):4736-4739
In this Letter we study the Friedel phase of the electron transport in two different systems of quantum dots which exhibit bound states in the continuum (BIC). The Friedel phase jumps abruptly in the energies of the BICs, which is associated to the vanishing width of these states, as shown by Friedrich and Wintgen in [H. Friedrich, D. Wintgen, Phys. Rev. A 31 (1985) 3964]. This odd behavior of the Friedel phase has consequences in the charge through the Friedel sum rule. Namely, if the energy of the BIC drops under the Fermi energy the charge changes abruptly in a unity. We show that this behavior closely relates to discontinuities in the conductance predicted for interacting quantum dot systems. 相似文献
20.
F. Findeis A. Zrenner M. Markmann G. Bhm G. Abstreiter 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We report about spatially resolved magneto-optical experiments on a self-assembled InGaAs quantum dot. Using electron beam lithograpy for patterning a metal shadow mask we can isolate a single dot. This allows us to study the optical response of a single dot as a function of excitation power and magnetic field. We investigate the influence of many body interaction in the emission spectra for different exciton occupation numbers of the dot. The diamagnetic/orbital shift as well as Zeeman splitting in a magnetic field can be fully resolved and are used to identify the observed emission lines. Further we report on absorption properties of the quantum dot as a function of magnetic field. We analyse in detail the phonon-assisted absorption process connected with the GaAs LO-phonon 36 meV above the single-exciton ground state. 相似文献