共查询到20条相似文献,搜索用时 15 毫秒
1.
Xia Yang Jun Xu Liujiang Xi Yanli Yao Qingdan Yang C. Y. Chung Chun-Sing Lee 《Journal of nanoparticle research》2012,14(6):1-6
One-dimensional ordered quantum-ring chains are fabricated on a quantum-dot superlattice template by molecular beam epitaxy. The quantum-dot superlattice template is prepared by stacking multiple quantum-dot layers and quantum-ring chains are formed by partially capping quantum dots. Partially capping InAs quantum dots with a thin layer of GaAs introduces a morphological change from quantum dots to quantum rings. The lateral ordering is introduced by engineering the strain field of a multi-layer InGaAs quantum-dot superlattice. 相似文献
2.
We have calculated the ground-state energy of the symmetric quantum-dot pattern by the ab initio calculation method, i.e. unrestricted Hartree-Fock-Roothaan (UHFR) method based on the Gaussian basis, and studied their electric capacitance spectra, assuming each quantum dot of quantum-dot pattern to be confined in a three-dimensional spherical potential well of finite depth. For the systems in question, our results show that our method and theoretical model not only give the electric capacitance peaks similar to s-shell and p-shell atom-like quantum dot, but also show some new fine-structure of electric capacitance in the symmetric quantum-dot pattern system. This method might be a feasible tool to study few-electron problems on the symmetric quantum-dot pattern system. 相似文献
3.
V. A. Kul’bachinskii R. A. Lunin V. A. Rogozin A. V. Golikov V. G. Kytin B. N. Zvonkov S. M. Nekorkin D. O. Filatov A. de Visser 《Physics of the Solid State》2003,45(4):762-767
The InAs/GaAs structures consisting of quantum-dot layers with electronic properties typical of two-dimensional systems are investigated. It is found that, at a low concentration of charge carriers, the variable-range-hopping conductivity is observed at low temperatures. The localization length corresponds to characteristic quantum-dot cluster sizes determined using atomic-force microscopy (AFM). The quantum Hall effect-insulator transition induced by a magnetic field occurs in InAs/GaAs quantum-dot layers with metallic conductivity. The resistivities at the transition point exceed the resistivities characteristic of electrons in heterostructures and quantum wells. This can be explained by the large-scale fluctuations of the potential and, hence, the electron density. 相似文献
4.
E.E. Onishchenko V.S. Bagaev V.V. Zaitsev E.I. Makhov 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):153
Studies of CdTe/ZnTe quantum-dot superlattices (self-assembled quantum-dot multilayers) have been carried out by optical spectroscopy methods in a wide range of temperatures. It has been shown that the ZnTe spacer layer thickness affects the properties of these quantum-dot superlattices due to changes in the elastic strain distribution pattern. An additional luminescence band appearing in the spectrum of the structure with the thinnest ZnTe spacer layer exhibits an anomalous shift of the peak position and an unusual behavior of integral intensity with the temperature increase. We assume that the spectrum of CdTe/ZnTe quantum-dot superlattices with the thinnest ZnTe spacer is caused by two kinds of excitonic states—spatially indirect and spatially direct. 相似文献
5.
采用离子束溅射技术制备了单层和双层Ge量子点, 通过原子力显微镜对比了不同Si隔离层厚度和不同掩埋量子点密度情况下表层量子点的尺寸和形貌差异, 系统研究了掩埋Ge量子点产生的应变对表层量子点的浸润层及形核的影响, 并用埋置应变模型对其进行解释. 实验结果表明, 覆盖Ge量子点的Si隔离层中分布着的应变场, 导致表层量子点浸润层厚度的降低, 从而增大点的体积; 应变强度随隔离层厚度的减小而增加, 造成表层量子点形状和尺寸的变化; 此外, 应变还调控了表层量子点的空间分布.
关键词:
Ge量子点
埋层应变
离子束溅射 相似文献
6.
B.?W.?Tilma M.?S.?Tahvili J.?Kotani R.?N?tzel M.?K.?Smit E.?A.?J.?M.?Bente 《Optical and Quantum Electronics》2009,41(10):735-749
Small signal modal gain measurements have been performed on two-section ridge waveguide InAs/InP (100) quantum-dot amplifiers
that we have fabricated with a peak gain wavelength around 1.70 μm. The amplifier structure is suitable for monolithic active-passive
integration, and the wavelength region and wide gain bandwidth are of interest for integrated devices in biophotonic applications.
A 65 nm blue shift of the peak wavelength in the gain spectrum has been observed with an increase in injection current density
from 1,000 to 3,000 A/cm2. The quantum-dot amplifier gain spectra have been analyzed using a quantum-dot rate-equation model that considers only the
carrier dynamics. The comparison between measured and simulated spectra shows that two effects in the quantum-dot material
introduce this large blue shift in the gain spectrum. The first effect is the carrier concentration dependent state filling
with carriers of the bound excited and ground states in the dots. The second effect is the decrease in carrier escape time
from the dots to the wetting layer with decreasing dot size. 相似文献
7.
Semiconductor quantum dots are among the leading candidates for next-generation nanoscale devices due to their tunable size, shape, and low energy consumption. Here we apply quantum optimal control theory to coherently manipulate the single-electron charge distribution in quantum-dot lattices of various sizes. In particular, we show that to control the charge distribution it is sufficient to optimize the gate voltage acting on a single quantum dot in the lattice. We generally find yields around 99% in the picosecond time scale when using realistic models for the quantum-dot lattices on a real-space grid. We analyze and discuss both the limitations of the model regarding the gate parameters as well as the potential of the scheme for applications as quantum-dot cellular automata. 相似文献
8.
用全量子理论导出隧穿量子点分子-辐射场相互作用系统状态满足的微分方程组, 在相干态辐射场和量子点分子处于隧穿激发态及基态的初始条件下, 应用Pegg-Barnett相位理论计算和分析了辐射场的相位概率分布及相位涨落, 研究了声子-量子点分子作用对辐射场相位的影响, 并与Husimi相位分布做了比较. 结果表明, 温度显著影响光场相位概率分布的时间演化规律, 声子既可以抑制也可以增强辐射场相位扩散和涨落, 取决于量子点分子的初态. Husimi相位分布和Pegg-Barnett相位分布符合度相当高.
关键词:
量子点分子
声子
量子相位
Q函数')" href="#">Q函数 相似文献
9.
We propose a scheme to engineer a non-local two-qubit
phase gate between two remote quantum-dot spins. Along with
one-qubit local operations, one can in principal perform various
types of distributed quantum information processing. The scheme
employs a photon with linearly polarisation interacting one after
the other with two remote quantum-dot spins in cavities. Due to the
optical spin selection rule, the photon obtains a Faraday rotation
after the interaction process. By measuring the polarisation of the
final output photon, a non-local two-qubit phase gate between the
two remote quantum-dot spins is constituted. Our scheme may has very
important applications in the distributed quantum information
processing. 相似文献
10.
Nobuyuki Fukui Hisato Yasumatsu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2013,67(4):1-4
We propose a scheme to implement controlled not gate for topological qubits in a quantum-dot and Majorana fermion hybrid system. Quantum information is encoded on pairs of Majorana fermions, which live on the the interface between topologically trivial and nontrivial sections of a quantum nanowire deposited on an s-wave superconductor. A measurement based two-qubit controlled not gate is produced with the help of parity measurements assisted by the quantum-dot and followed by prescribed single-qubit gates. The parity measurement, on the quantum-dot and a topological qubit, is achieved by the Aharonov-Casher effect. 相似文献
11.
Geza Toth Craig S. Lent P.Douglas Tougaw Yuriy Brazhnik Weiwen Weng Wolfgang Porod Ruey-Wen Liu Yih-Fang Huang 《Superlattices and Microstructures》1996,20(4):473-478
We have previously proposed a way of using coupled quantum dots to construct digital computing elements—quantum-dot cellular automata. Here we consider a different approach to using coupled quantum-dot cells in an architecture which, rather than reproducing Boolean logic, uses a physical near-neighbor connectivity to construct an analog cellular neural network. 相似文献
12.
The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor. 相似文献
13.
Three topics related to correlated electrons in coupled quantum dots are discussed. The first is quasi-resonance between multi-electron states, which causes hitherto unremarked types of resonant absorption in coupled quantum dots. The second is electron tunneling through a Hubbard gap, which is induced by an increase in the density of electrons in a quantum-dot chain under an overall confining potential. The third is Mott transition in a two-dimensional quantum-dot array induced by an external electric field. In this system, the metal-insulator transition goes through a heavy electron phase in which the density of correlated electrons fluctuates. 相似文献
14.
The observation of quantum-dot resonance fluorescence enabled a new solid-state approach to generating single photons with a bandwidth approaching the natural linewidth of a quantum-dot transition. Here, we operate in the small Rabi frequency limit of resonance fluorescence--the Heitler regime--to generate subnatural linewidth and high-coherence quantum light from a single quantum dot. The measured single-photon coherence is 30 times longer than the lifetime of the quantum-dot transition, and the single photons exhibit a linewidth which is inherited from the excitation laser. In contrast, intensity-correlation measurements reveal that this photon source maintains a high degree of antibunching behavior on the order of the transition lifetime with vanishing two-photon scattering probability. Generating decoherence-free phase-locked single photons from multiple quantum systems will be feasible with our approach. 相似文献
15.
The size distribution functions for nanoclusters in quantum-dot heterostructures are calculated within the LSW theory. The
most common numerical characteristics are calculated for these distributions. The corresponding size distribution functions
are selected by means of comparison of the calculated dispersion and mean square deviation with the experimental values obtained
for real quantum-dot heterostructures. The regularities of variations of certain numerical characteristics as a function of
growth mechanism are shown for different distributions, from the well-known modified Wagner and Lifshitz-Slezov distributions
to the distributions proposed in this work.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 59–66, April, 2006. 相似文献
16.
V. S. Vinogradov G. Karczewski I. V. Kucherenko N. N. Mel’nik P. Fernandez 《Physics of the Solid State》2008,50(1):164-167
Quantum-dot structures based on the CdTe, ZnTe, and CdSe semiconductors are prepared by molecular-beam epitaxy, colloid chemistry methods, and ball milling, and their Raman spectra are studied. Localized longitudinal phonons are observed in all spectra. The dependence of the localized phonon frequency on the thickness of the ZnTe barrier in CdTe/ZnTe quantum-dot superlattices is used to derive the dispersion relation for longitudinal phonons in ZnTe. The Raman spectra of ensembles of colloidal quantum dots differ from the spectra of the other objects by the absence of tellurium bands and a strong intensity of the longitudinal phonon band of CdTe. It is revealed that the spectra depend on the technology employed to prepare quantum-dot structures. 相似文献
17.
The dynamical localization phenomena in two-electron quantum-dot shuttles driven by an ac field have been investigated and analyzed by the Floquet theory. The dynamical localization occurs near the anti-crossings in Floquet eigenenergy spectrum. The oscillation of the quantum-dot shuttles may increase the possibility of the dynamical localization. Especially, even if the two electrons are initialized in two neighbor dots, they can be localized there for appropriate intensity of the driven field. The studies may help the understanding of dynamical localization in electron shuttles and expand the application potential of nanoelectromechanical devices. 相似文献
18.
Sukhovatkin V Musikhin S Gorelikov I Cauchi S Bakueva L Kumacheva E Sargent EH 《Optics letters》2005,30(2):171-173
We report room-temperature amplified spontaneous emission and spectral narrowing at infrared wavelengths in solution-processed films made up of PbS quantum-dot nanocrystals. The results are relevant to optical amplification and lasing integrated upon a variety of substrates. The active optical medium operates at room temperature without any additional matrix material, providing an optical gain of 260 cm(-1) and a pump threshold of 1 mJ/cm(-2). Nanocrystals synthesized in an aqueous solution and stabilized by use of short ligands result in high quantum-dot volume fractions in solid films and in a redshift emission relative to absorption. 相似文献
19.
A steady-state rate-equation model for temperature-dependent luminescence spectra from localized-state material system is presented. The effects of thermal emission, recapturing, radiative and nonradiative recombination are taken into account in the model. Two localized-state material systems, including InAs/GaAs quantum-dot and InGaN/GaN-multi-quantum-well samples were prepared. It is found that the temperature-dependent behaviors of luminescence emission energy obtained from the two samples are quite different. In the mid-temperature range, the emission peaks exhibit a redshift for quantum-dot sample, but a blueshift for multi-quantum-well sample. The peak energies of the luminescence spectra are simulated in this model and show a good agreement with experiment. The corresponding luminescence mechanisms of carriers in localized-state material systems, which lead to the diversity are quantitatively discussed in detail by the model. 相似文献
20.
《Superlattices and Microstructures》1998,23(5):1103-1106
We present Raman-scattering results for CdTe nanocrystals in doped glasses which clearly show the confinement effects on the phonon spectra as a function of the quantum-dot size. We observed optical phonon modes, surface phonons and some of their overtone combinations. We show that the surface-phonon scattering intensity increases as the quantum-dot size decreases. Our results also show a decrease in the electron–phonon coupling as the nanocrystal size is decreased. These confinement effects are observed by changing the laser excitation energy, and thus by tuning to resonance with the optical transitions for quantum dots of different sizes within their broad size distribution in semiconductor-doped glasses. 相似文献