半导体自组织量子点量子发光机理与器件

介绍了自组织量子点单光子发光机理及器件研究进展.主要内容包括：半导体液滴自催化外延GaAs纳米线中InAs量子点和GaAs量子点的单光子发光效应、自组织InAs/GaAs量子点与分布布拉格平面微腔耦合结构的单光子发光效应和器件制备,单量子点发光的共振荧光测量方法、量子点单光子参量下转换实现的纠缠光子发射、单光子的量子存储效应以及量子点单光子发光的光纤耦合输出芯片制备等.     

Temperature dependent growth of InGaN/GaN single quantum well

InGaN/GaN single quantum well (SQW) structures under various InGaN growth temperatures have been grown by metal organic chemical vapor deposition (MOCVD), the surface morphologies and optical properties are investigated. The radius of the typical V-pits on the SQW surface is affected by the InGaN well-temperature, and the surface roughness decreased as the well-temperature reduced. Room-temperature photoluminescence (PL) and cathode luminescence (CL) shows the quantum well and quantum dot (QD)-like localized state light emission of the SQWs grown at 700 and 690 °C, respectively, whereas the samples grown at 670 and 650 °C present hybrid emission peaks. Excitation power dependent PL spectra indicates the QD-like localized state emission dominates at low excitation power and the quantum well emission starts to take over at high excitation power.     

Quantum information transfer between topological and conventional charge qubits

We propose a scheme to realize coherent quantum information transfer between topological and conventional charge qubits. We first consider a hybrid system where a quantum dot(QD) is tunnel-coupled to a semiconductor Majorana-hosted nanowire(MNW) via using gated control as a switch, the information encoded in the superposition state of electron empty and occupied state can be transferred to each other through choosing the proper interaction time to make measurements.Then we consider another system including a double QDs and a pair of parallel MNWs, it is shown that the entanglement information transfer can be realized between the two kinds of systems. We also realize long distance quantum information transfer between two quantum dots separated by an MNW, by making use of the nonlocal fermionic level formed with the pared Majorana feimions(MFs) emerging at the two ends of the MNW. Furthermore, we analyze the teleportationlike electron transfer phenomenon predicted by Tewari et al. [Phys. Rev. Lett. 100, 027001(2008)] in our considered system.Interestingly, we find that this phenomenon exactly corresponds to the case that the information encoded in one QD just returns back to its original place during the dynamical evolution of the combined system from the perspective of quantum state transfer.     

Quantum correlation dynamics of two qubits in independent reservoirs with initial system-reservoir correlations

The dynamics of entanglement and quantum discord(QD) between two two-level atoms interacting with two dissipative coupled cavities in the presence of initial atom-cavity correlations is investigated. In comparison with the result of the initial factorized state, we show that the initial state contained quantum correlation of atom-cavity is most robust against the dissipative environment, and the initial atom-cavity correlations, especially the quantum correlation, play a constructive role in the generation of atomic entanglement and QD.Simultaneously, the comparison between Markovian and non-Markovian dynamics, and the influences of inter-cavity hopping rate are also taken into account and analyzed.     

Spontaneous emission of quantum dot excitons into surface plasmons in a nanowire

The spontaneous emission (SE) of quantum dot (QD) excitons into surface plasmons in a cylindrical nanowire is investigated theoretically. Maxwell's equations with appropriate boundary conditions are solved numerically to obtain the dispersion relations of surface plasmons. The SE rate of QD excitons is found to be greatly enhanced at certain values of the exciton bandgap. Application in generation of remote entangled states via superradiance is also pointed out and may be observable with current technology.     

Enhancement or quenching effect of metallic nanodimer on spontaneous emission

The plasmonic effects of a metallic (Au or Ag) nanodimer on the excitation and emission of a single emitter placed within the gap of the nanodimer are studied to identify its overall performance (enhancement or quenching) for the spontaneous emission. The process of a spontaneous emission is divided into two stages for analysis: the excitation and the subsequent emission stages. For the excitation stage, the amplification of the local electric field around the gap region is studied to show the converging-lens effect of the nanodimer for focusing an incident light. For the emission stage, the apparent quantum yield of an electric dipole (the excited emitter) in the presence of the nanodimer is studied in terms of its radiative and nonradiative decay rates. Both models are simulated by the multiple multi-pole methods for solving Maxwell's equations. The results indicate that the overall enhancement factor of a metallic nanodimer on the spontaneous emission depends not only on its dimension (radius and gap) but also on the absorption and emission spectra of the emitter. Moreover, there is an optimal dimension (radius and gap) of a nanodimer for obtaining the maximum enhancement to a specific spontaneous emission. In addition, the observed emission spectrum of the emitter can be modified by the nearby nanodimer (a low-pass filter), and its lifetime can be reduced by two or three orders of magnitude due to the energy transfer between them.     

Near‐field optical enhancement by lead‐sulfide quantum dots and metallic nanoparticles for SERS

There is a growing interest in using quantum dots (QDs) and metallic nanoparticles (NPs), both for luminescence enhancement and surface‐enhanced Raman scattering (SERS). Here, we study the electromagnetic‐field enhancement that can be generated by lead‐sulfide (PbS) QDs using three‐dimensional finite‐element simulations. We investigate the field enhancement associated with combinations of PbS QDs with metallic NPs and substrates. The results show that high field enhancement can be achieved by combining PbS QDs with metallic NPs of larger sizes. The ideal size for Ag NPs is 25 nm, providing a SERS enhancement factor of ~5*10⁸ for light polarization parallel to the NP dimer axis and a gap of 0.6 nm. For Au NPs, the bigger the size, the higher is the field for the studied diameters, up to 50 nm. The near‐field values for PbS QDs above metallic substrates were found to be lower compared to the case of PbS QD‐metal NP dimers. This study provides the understanding for the design and application of QDs for the enhancement of near‐field phenomena. Copyright © 2013 John Wiley & Sons, Ltd.     

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots(QDs) are fabricated on Si nanowires(NWs) substrates with and without Au nanoparticles(NPs). The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence(PL) intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.     

Optimum Quantum Yield of the Light Emission from 2 to 10 nm Hydrosilylated Silicon Quantum Dots

Optimizing the light‐emitting efficiency of silicon quantum dots (Si QDs) has been recently intensified by the demand of the practical use of Si QDs in a variety of fields such as optoelectronics, photovoltaics, and bioimaging. It is imperative that an understanding of the optimum light‐emitting efficiency of Si QDs should be obtained to guide the design of the synthesis and processing of Si QDs. Here an investigation is presented on the characteristics of the photoluminescence (PL) from hydrosilylated Si QDs in a rather broad size region (≈2–10 nm), which enables an effective mass approximation model to be developed, which can very well describe the dependence of the PL energy on the QD size for Si QDs in the whole quantum‐confinement regime, and demonstrates that an optimum PL quantum yield (QY) appears at a specific QD size for Si QDs. The optimum PL QY results from the interplay between quantum‐confinement effect and surface effect. The current work has important implications for the surface engineering of Si QDs. To optimize the light‐emission efficiency of Si QDs, the surface of Si QDs must be engineered to minimize the formation of defects such as dangling bonds at the QD surface and build an energy barrier that can effectively prevent carriers in Si QDs from tunneling out.     

金属微结构纳米线中等离激元传播和分光特性

本文从理论和实验两方面探讨了具有微结构的金属纳米线系统中表面等离激元传播规律和分光特性. 我们由麦克斯韦方程组出发, 利用严格耦合波近似和有限元差分等方法首先从理论上给出了金属纳米线系统中等离激元的色散关系和能带特征, 然后基于微结构的银纳米线及其等离激元能带结构, 设计并制备出等离激元分光原型器件, 实验展示其将不同频率的光在微小空间分离的特性. 该研究结果是我们前期相关工作的延续和补充, 可应用于构造多功能集成的光子芯片和新型亚波长光电材料和器件.     

Optimizing the top profile of a nanowire for maximum forward emission

The optimal top structure of a nanowire quantum emitter single photon source is significant in improving performance. Based on the axial symmetry of a cylindrical nanowire, this paper optimizes the top profile of a nanowire for the maximum forward emission by combining the geometry projection method and the finite element method. The results indicate that the nanowire with a cambered top has the stronger emission in the forward direction, which is helpful to improve the photon collection efficiency.     

Luminescent ‘On-Off’ CdSe/ZnS Quantum Dot Chemodosimeter for Hydroxide Based on Photoinduced Electron Transfer from a Carboxylate Moiety

A CdSe-ZnS quantum dot (QD) has been surface functionalised by a place exchange reaction with p-mercaptomethyl benzoate synthesized by a three-step procedure. The resulting lumophore-spacer-receptor QD-conjugate was characterized by IR, UV-visible and fluorescence spectroscopy. The emission profile of the QD reveals a narrow emission peak centred at 542 nm. Addition of hydroxide to the solution containing the QD-conjugate results in quenching of the original fluorescence, which is attributed to a photoinduced electron transfer reaction from the electron-rich benzoate moiety to the QD valence band. This is the first reported example of fluorescent quenching of a CdSe-ZnS QD luminescence by an aryl carboxylate moiety.     

The quantum yield of a metallic nanoantenna

The local-field factor and quantum yield of a metallic nanoantenna are studied to identify its enhancement of an emitter’s emission within the feed gap. For simplicity, a two-dimensional model, an Au nanoantenna with an emitter at the center, is studied. The electromagnetic field is solved by a set of surface integral equations. An incident plane wave irradiating the nanoantenna is modeled to simulate the excitation of the emitter by illuminating light, and the local-field factor is used to evaluate the amplification of the electric field in the feed gap of the metallic nanoantenna. Once the emitter becomes excited, a model of an electric dipole interacting with the nanoantenna is used for calculating the radiative and nonradiative powers to obtain the quantum yield of the excited emitter in the presence of the nanoantenna. The numerical results of quantum yield indicate that an Au nanoantenna acts as a low-pass filter for the emission of the emitter. Moreover, the smaller the feed gap, the larger the local-field factor but the less the quantum yield. PACS 78.67.-n; 33.80.-b; 33.50.-j; 42.30.-d; 42.50.Hz; 81.07.Pr     

量子点操控的光子探测和圆偏振光子发射

半导体量子点是研究光子与电子态相互作用的优选固态体系,并在光子探测和发射两个方向上展现出独特的技术机遇.其中基于量子点的共振隧穿结构被认为在单光子探测方面综合性能最佳,但受到光子数识别、工作温度两个关键性能的制约.利用腔模激子态外场耦合效应,有望获得圆偏振态可控的高频单光子发射.本文介绍作者提出的量子点耦合共振隧穿（QD-cRTD）的光子探测机理,利用量子点量子阱复合电子态的隧穿放大,将QD-cRTD光子探测的工作温度由液氦提高至液氮条件,光电响应的增益达到10⁷以上,并具备双光子识别能力;同时,由量子点能级的直接吸收,原型器件获得了近红外的光子响应.在量子点光子发射机理的研究方面,作者实现了量子点激子跃迁和微腔腔模共振耦合的磁场调控,在Purcell效应的作用下增强激子自旋态的自发辐射速率,从而增强量子点中左旋或右旋圆偏振光的发射强度,圆偏度达到90%以上,形成一种光子自旋可控发射的新途径.     

Oxide/polymer nanocomposites as new luminescent materials

It is demonstrated that nanocomposites, consisting of an electrically insulating oxide core and PMMA coating exhibit strong luminescence. This luminescence is connected to the interface, where PMMA is bond via a carboxylate bonding to the surface. In this case, luminescence is originated at the carbonyl group of the coating polymer. With decreasing particle size, this emission shows a blue shift, following a law inversely the ones found for quantum confinement systems. For semi-conducting oxides, such as ZnO, this interface related emission is found additionally to quantum confinement phenomena.     

Advances in photonic crystals with MEMS and with semiconductor quantum dots

We discuss photonic crystals (PCs) with a microelectromechanical system (MEMS) and semiconductor quantum dots (QDs) as novel classes of PC devices. Integration of MEMS structures into PC devices enables one to realize several kinds of functional devices, such as modulators, switches, and tunable filters for highly integrated photonic circuits. We describe the basic concept of MEMS-integrated PC devices and show numerical and experimental demonstrations of MEMS-integrated functional PC devices. On the other hand, QDs are promising candidates for active media in PC devices. Spontaneous emission control of QD emission in PC nanocavities is especially important for novel optoelectronic devices and quantum information devices. In PC nanocavities, the interaction between QD excitons and photons is enhanced dramatically. The control of spontaneous emission spectrum and the enhancement of the luminescence intensity of InAs QDs by PC nanocavities are demonstrated at telecommunication wavelengths. The Purcell effect for ensemble and single QDs in PC nanocavities are also discussed.     

Characterizing Quantum Correlations in Arbitrary-Dimensional Bipartite Systems Using Hurwitz's Theory

Quantum correlations play vital roles in the quantum features in quantum information processing tasks. Among the measures of quantum correlations, quantum discord （QD） and entanglement of formation （EOF） axe two significant ones. Recent research has shown that there exists a relation between QD and EOF, which makes QD more significant in quantum information theory. However, until now, there exists no general method of chaxaeterizing quantum discord in high-dimensional quantum systems. In this paper, we have proposed a general method for calculating quantum discord in axbitraxy-dimensionM bipaxtite quantum systems in terms of Hurwitz＇s theory. Applications including the Werner state, the spin-1 XXZ model thermal equilibrium state, the Horodecki state, and the separable-bound-free entanglement state are investigated. We present the method of obtaining the EOF of axbitraxy-dimensional bipaxtite quantum states via purification, and the relations.hip between QD and EOF.     

Hidden Vacuum Rabi Oscillations:Dynamical Quantum Superpositions of On/Off Interaction between a Single Quantum Dot and a Microcavity

We show that it is possible to realize quantum superpositions of switched-on and-off strong light-matter interaction in a single quantum dot-semiconductor microcavity system.Such superpositions enable the observation of counterintuitive quantum conditional dynamics effects.Situations are possible where cavity photons as well as the emitter luminescence display exponential decay but their joint detection probability exhibits vacuum Rabi oscillations.Remarkably,these quantum correlations are also present in the nonequilibrium steady state spectra of such coherently driven dissipative quantum systems.     

Energy transfer in associates of semiconductor quantum dots with tetrapyridinoporphyrazine molecules

The interaction of CdSe/ZnS quantum dots (QDs) with metal-free tetrapyridinoporphyrazine (TPPA) molecules in chloroform has been investigated. It was found that, at QD concentrations lower than ～3 × 10^?7 M, QD luminescence is quenched in the presence of TPPA and characteristic changes occur in the absorption and luminescence spectra of TPPA, which reflect the interaction of TPPA molecules with the QD surface. Along with the QD luminescence quenching, sensitized luminescence of TPPA molecules adsorbed on QDs was observed. The luminescence excitation spectra of adsorbed TPPA molecules unambiguously indicate the presence of energy transfer from QDs to TPPA. The efficiency of energy transfer from QDs to TPPA is estimated from the quantum yield of sensitized TPPA luminescence.     

闪锌矿GaN/AlGaN量子点中激子态及光学性质的研究

在有效质量近似的框架下,运用变分方法研究闪锌矿GaN/AlGaN量子点中的激子态及相关光学性质,探讨电子与空穴在量子点中的三维空间受限和有限势效应.数值计算结果显示,当量子点的尺寸增加时, 量子尺寸效应对电子和空穴的影响减弱,基态激子结合能和带间光跃迁能也都降低;而当该量子点中垒层AlGaN中 Al含量增加时,提高了量子点对电子和空穴的束缚作用, 同时基态激子结合能和带间光跃迁能都增加.数值的理论结果与相关实验测量结果一致.