多功能高分子修饰PbS量子点光纤放大器

创新性地合成了一种新型多功能高分子用于改变 PbS量子点表面的配体极性。利用高分子末端的羧基与PbS量子点之间较强的络合作用,通过配体交换替换PbS量子点表面原有的油胺配体。通过这种方法修饰PbS量子点步骤简便,而且很好的保持了PbS量子点的荧光效率。经过配体交换以后的PbS量子点可以转移至极性溶剂中,提高了PbS量子点在极性溶剂中稳定性,并利用生长法将配体交换后的 PbS量子点生长于锥形单模光纤耦合器表面,制成光纤放大器。随后,研究了高分子中氟成分对于信号增益的影响,结果表明随着高分子中氟含量的增加,信号增益越大,证明这种高分子修饰的量子点在光纤放大器方面会有更好的应用前景。     

氧化物薄膜抑制量子点的光衰性能

量子点应用于LED中,可获得高饱和性、宽色域光源,在液晶显示背光源领域前景广阔。但是,影响量子点寿命的因素很多,如温度、水氧等,严重阻碍了其推广应用。目前,水氧对量子点光衰性能影响的研究较少,本文旨在研究无机氧化物薄膜阻隔层对量子点光衰性能的影响。量子点成膜后表面溅射Al2O3、SiO2水氧隔离薄膜,蓝光LED激发绿光量子点,研究其光衰性能。结果表明,与无隔离膜的样品相比,单层SiO2薄膜的样品光衰性能有所改善;双层的SiO2薄膜及SiO2/Al2O3复合薄膜,可以有效地减小薄膜孔洞大小和孔洞密度,阻隔水氧的进入,抑制量子点的光衰减,提高量子点寿命。     

Nanophotonics: Application of Dressed Photons to Novel Photonic Devices and Systems

This paper reviews recent progress in nanophotonics, a novel optical technology proposed by one of the authors (M. Ohtsu). Nanophotonics utilizes the local interaction between nanometric particles via optical near fields. The optical near fields are the elementary surface excitations on nanometric particles, that is, dressed photons that carry the material energy. Of the variety of qualitative innovations in optical technology realized by nanophotonics, this paper focuses on devices and systems. The principles of device operation are reviewed considering the excitation energy transfer via the optical near-field interaction and subsequent dissipation. As representative examples, the principles of a nanophotonic and gate, not gate, and optical nanofountain are described. Experimental results for operating devices using CuCl quantum dots (QDs), InAlAs QDs, and nanorod ZnO double quantum wells are described. Using a systems-perspective approach, the principles of content-addressable memory based on nanophotonic device operations and experimental results are reviewed. The hierarchy of optical near-field interactions is discussed, and its application to a multilayer memory retrieval system is demonstrated.      

Microscopic modeling of gain and luminescence in semiconductors

The capabilities of a fully microscopic approach for the calculation of optical material properties of semiconductor lasers are reviewed. Several comparisons between the results of these calculations and measured data are used to demonstrate that the approach yields excellent quantitative agreement with the experiment. It is outlined how this approach allows one to predict the optical properties of devices under high-power operating conditions based only on low-intensity photo luminescence (PL) spectra. Examples for the gain-, absorption-, PL- and linewidth enhancement factor-spectra in single and multiple quantum-well structures, superlattices, Type II quantum wells and quantum dots, and for various material systems are discussed.     

Anisotropic Quantum Dots

This paper presents a detailed calculation of the electronic structure of quantum dots with various geometries. In particular, non-circular quantum dots are examined and their characteristic properties analysed. A general matrix method was developed that allows us to treat a wide range of quantum dots with arbitrarily complex confinement potentials. The Hartree-Fock self-consistent method is applied to study quantum dots with many-electrons.     

Selective growth of InAs quantum dots by metalorganic chemical vapor deposition

We report results of both strain-driven surface segregation of indium from InGaAs thin films as well as selective area epitaxy of InAs quantum dots using these films. InAs segregation from an underlying InGaAs film allows for preferential growth of quantum dots when additional InAs is deposited. By using standard lithography techniques, a two-step selective growth process for quantum dots is achieved. Furthermore, by utilizing self-assembled nanostructures as a template, selective growth of coalesced wires and dots with 100-nm feature sizes are realized.     

Effects of substrate orientation on opto-electronic properties in self-assembled InAs/GaAs quantum dots

Electronic structure and optical transition characteristics in (100), (110), and (111) oriented InAs/GaAs quantum dots (containing \({\sim }2\) million atoms) were studied using a combination of valence force-field molecular mechanics and 20-band \(sp^{3}d^{5}s^{*}\) atomistic tight-binding framework. These quantum dots are promising candidates for non-traditional applications such as spintronics, quantum cryptography and quantum computation, but suffer from the deleterious effects of various internal fields. Here, the dependence of strain and polarization fields on the substrate orientation is reported and discussed. It is found that, compared to the (100) and (110) oriented counterparts, quantum dots grown on the (111) oriented substrate exhibit a smaller splitting (non-degeneracy) in the excited \(P\) states and enhanced isotropy in the interband optical emission characteristics.     

Optical and Electrical Properties of Colloidal Quantum Dots in Electrolytic Environments: Using Biomolecular Links in Chemically-Directed Assembly of Quantum Dot Networks

The threshold of the absorption spectra of colloidal cadmium sulfide (CdS) quantum dots in electrolytic solutions is shown to shift as the concentration of the electrolyte is varied. The shift in the absorption threshold as a function of the electrolytic concentration is given by electrolytic screening of the field caused by the intrinsic spontaneous polarization of these würtzite quantum dots. These electrolyte-dependent absorption properties are compared with Fermi-level tuning in carbon nanotubes in electrolytic environments.Moreover, concepts for integrating such colloidal quantum dots in high density networks with biomolecular links are discussed. Such biomolecular links are used to facilitate the chemically-directed assembly of quantum dots networks with densities approximating 10¹⁷ cm⁻³.     

Materials for Photonic Applications From Sol-Gel*

A review of sol-gel materials developed in our laboratory for photonic applications is presented. These materials include planar and strip waveguides for integrated optics (IO) passive devices, Er doped waveguides for IO amplifiers, films doped with semiconductor quantum dots for optical switching and fullerene doped materials for optical limiting.     

Materials for Photonic Applications From Sol-Gel*

A review of sol-gel materials developed in our laboratory for photonic applications is presented. These materials include planar and strip waveguides for integrated optics (IO) passive devices, Er doped waveguides for IO amplifiers, films doped with semiconductor quantum dots for optical switching and fullerene doped materials for optical limiting.     

Improved luminescence from quantum-dot nanostructures embedded in structurally engineered (In,Ga)As confining layers

Efficient luminescence of quantum-dot nanostructures embedded in active regions of lasers is important for low-threshold current density devices. This paper discusses an approach for structurally engineering confining (In,Ga)As layers into which InAs quantum dots are inserted to enhance their emission efficiency. It is shown that by inserting the dots at the center of compositionally graded In/sub x/Ga/sub 1-x/As layers, the relative emission efficiency can be increased by nearly an order of magnitude over the emission of dots inside a constant composition (In,Ga)As structure. This enhancement is thought to be a result of the high structural and optical quality of the confining layers.     

Development of IR-emitting colloidal II-VI quantum-dot materials

The current state-of-the-art of colloidal II-VI nanocrystal formation using the aqueous/thiol synthesis route is described. Work on single component and heterostructures and mixed compound quantum dots is discussed. The purpose of the work is to provide a range of infrared (IR)-emitting materials with high quantum efficiency (QE) as potential gain media for future ultrawideband optical amplifiers for high-capacity wavelength-division multiplexing (WDM) telecommunications systems. Physical and chemical factors influencing particle sizes are described     

GaN基多量子阱蓝色发光二极管的实验与理论分析

本研究采用量子点模型对蓝色InGaN/GaN多量子阱发光二极管电致发光光谱进行考察,并和实验测量结果进行了比对。结果发现,利用量子点模型计算出的自发辐射发光峰位与实验得出的电致发光的峰位很好地吻合,表明了在多量子阱发光二极管中由于InN和GaN相分离而形成的富In类量子点结构,主导着InGaN基发光二极管发光波长,体现了InGaN基发光二极管量子点发光的本质。同时,基于量子点模型的理论,本文讨论了以合适组分的四元A lInGaN材料取代传统的GaN材料作为量子阱垒层对发光二极管发光特性的影响。     

Near-field spectroscopy of a single InGaAs self-assembled quantumdot

Relaxation mechanism of excited carriers in InGaAs-GaAs self-assembled quantum dots has been investigated. Near-field photoluminescence excitation (PLE) spectra show some sharp resonance lines whose energies match those of the LO phonons observed in far-field PLE. The results suggest that the PLE resonant peaks are predominantly due to resonant Raman scattering from phonons. This assignment is consistent with the absence of magnetic field dependence of the resonances. Single dot coherent spectroscopy shows the dephasing time of resonant carriers to be as fast as several tens of picoseconds. This fast dephasing time agrees with the phonon-electron interactions being strong. These results allow better understanding of the carrier relaxation process in InGaAs-GaAs self-assembled quantum dots     

Transmission coefficients for minibands formed in quantum dot arrays under bias

Arrays of colloidal quantum dots have a number of potential optoelectronic applications that depend on the efficiency of carrier collection form the matrix-embedded array of quantum dots. Herein, carrier transmission coefficients are calculated for bound states and quasi-bound states in a 3-dimensional superlattice formed by an alternating structure of colloidal quantum dots and matrix materials, including conductive polymers.     

Quantum dot blinking: relevance to physical limits for nanoscale optoelectronic device

In designing nanoscale optoelectronic devices based on a small number of active quantum dots, it is of interest to consider that semiconductor nanocrystals (quantum dots) are observed to blink “on” and “off”. The time probability distributions scale as an inverse power law for colloidal quantum dots and exponentially for self-assembled dots. Possible mechanisms that cause the inverse power law and exponential blinking statistics are discussed in the paper and the relevance to quantum-dot based system architectures is discussed.     

3D simulation of a silicon quantum dot in a magnetic field based on current spin density functional theory

We have developed a code for the simulation of the electrical and magnetic properties of silicon quantum dots in the framework of the TCAD Package NANOTCAD-ViDES. We adopt current spin density functional theory with a local density approximation and with the effective mass approximation. We show that silicon quantum dots exhibit large variations of the total spin as the number of electrons in the dot and the applied magnetic field are varied. Such properties are mainly due to the silicon band structure, and make silicon quantum dots interesting systems for spintronic and quantum computing experiments.     

New schemes for creating large optical Schrödinger cat states using strong laser fields

Recently, using conditioning approaches on the high-harmonic generation process induced by intense laser-atom interactions, we have developed a new method for the generation of optical Schrödinger cat states (Lewenstein et al. in Nat Phys, 17 1104–1108, 2021. https://doi/10.1038/s41567-021-01317-w). These quantum optical states have been proven to be very manageable as, by modifying the conditions under which harmonics are generated, one can interplay between kitten and genuine cat states. Here, we demonstrate that this method can also be used for the development of new schemes towards the creation of optical Schrödinger cat states, consisting of the superposition of three distinct coherent states. Apart from the interest these kind of states have on their own, we additionally propose a scheme for using them towards the generation of large cat states involving the sum of two different coherent states. The quantum properties of the obtained superpositions aim to significantly increase the applicability of optical Schrödinger cat states for quantum technology and quantum information processing.

     

Towards understanding the superfluid behavior in double layer graphene nanostructures

The unique electronic properties that are found in graphene layers have been touted as an attractive means to not only study fundamental physical principles but to design new types of electronic and optical information processing technologies. Of the physical observables present in graphene which may be exploited for device technologies, the proposed superfluid phase transition of indirectly bound excitons in closely spaced layers of graphene is one of the most exciting. Nevertheless, the superfluid phase of double layer graphene remains a poorly understood quantity. In this work, we theoretically investigate the properties of the superfluid phase in double layer graphene systems via two disparate methods: path-integral quantum Monte Carlo and non-equilibrium Green’s functions. We show that the superfluid phase in double layer graphene persists up to ambient temperatures in spinless systems. When we increase the number of degrees of freedom in the system to include spin, we find that the screening effectiveness is suppressed by intralayer correlations resulting in higher transition temperatures than previously predicted. Furthermore, we estimate the magnitude of the interlayer currents that the superfluid can sustain under non-ideal conditions by considering the effects of layer disorder and the electron-phonon interaction. We show that the superfluid dynamics is significantly affected not only by the total amount of disorder but also depends very heavily on the location of the disorder in the layers. When the electron-phonon interaction is included, we demonstrate that for high layer carrier densities the electron-phonon interaction does not affect superfluid flow but degrades the transport properties significantly as the layer carrier concentration decreases.     

Exciton relaxation and dephasing in quantum-dot amplifiers from room to cryogenic temperature

We present an extensive experimental study of the exciton relaxation and dephasing in InGaAs quantum dots (QDs) in the temperature range from 10 K to 295 K. The QDs are embedded in the active region of an electrically pumped semiconductor optical amplifier. Ultrafast four-wave mixing and differential transmission spectroscopy on the dot ground-state transition are performed with a sensitive heterodyne detection technique. The importance of the population relaxation dynamics to the dephasing is determined as a function of injection current and temperature. Above 150 K dephasing processes much faster than the population relaxation are present, due to both carrier-phonon scattering and Coulomb interaction with the injected carriers. Only at low temperatures (<30 K) does population relaxation of multiexcitons in the gain regime fully determine the dephasing.