Formation and Properties of New Types of Metal–Dielectric Nanostructures for Creating Optical Metamaterials

Semiconductors - “Herein, we consider the technologies of obtaining composite structures that can exhibit the properties of metamaterials, namely layered metal–dielectric...     

Capacitance Spectroscopy of Heteroepitaxial AlGaAs/GaAs p–i–n Structures

Semiconductors - The temperature dependences of the capacitance-voltage (C–V) characteristics and deep-level spectra of a graded high-voltage AlxGa1 – xAs p0–i–n0 junction...     

Understanding Dopant–Host Interactions on Electronic Structures and Optical Properties in Ce-Doped WS2 Monolayers

Substitutional lanthanide doping of 2D transition metal dichalcogenides (TMDs) is expected to be a promising strategy to engineer optical, electronic, and optoelectronic properties of TMDs. Understanding the interactions between lanthanide dopants and 2D TMDs host is one of the key problems to be resolved for their profound research studies. Herein, the interactions between Ce dopants and monolayer WS₂ in a physical vapor deposition grown Ce-doped WS₂ monolayer are studied by combining scanning tunneling microscopy with optical characterizations with high spatial and temporal resolution. It is found that the highly anisotropic crystal field can effectively split the energy levels of the Ce dopants’ f orbital. The electrons in the split energy levels can bind the holes in the valence band maximum of the Ce-doped WS₂, forming optical bright excitons. These excitons collide with the free A excitons when increasing the pump fluences, reducing the A exciton's lifetime. This study may be beneficial for the design and fabrication of optical, electronic, and optoelectronic devices based on lanthanide-doped TMDs.     

Electrical and Optical Properties of Unrelaxed InAs1 –xSbx Heteroepitaxial Structures

Semiconductors - The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs1 –xSbx structures (x = 0.43 and 0.38) in a wide temperature range of 5–300 K and...     

Excitonic Effects and Impurity–Defect Emission in GaAs/AlGaAs Structures Used for the Production of Mid-IR Photodetectors

Semiconductors - A series of undoped GaAs/AlxGa1 –xAs multiple quantum well heterostructures, whose doped analogs are used for the production of photodetectors operating in the spectral range...     

Design and Optimization of Quasi–Optical Frequency Multipliers

This paper presents a full–wave algorithm for the design and the optimization of quasi–optical frequency multipliers and discusses its implementation in a specialized computer code, able to simulate as a whole the non–linear device, the planar antenna and the embedding layered structure. The electromagnetic analysis of the multiplier is performed under the simplifying approximation of an infinite array excited by a uniform plane wave incident from the broadside direction. The array parameters are deduced from a full–wave analysis, based on the Method of the Moments, while the solution of the non–linear circuit is found by the Harmonic Balance Method.     

Optical and thermal properties of precursor-controlled graphene–zinc nanocomposites

Graphene, a monolayer two dimensional carbon sheet can be utilized as a support to anchor functional nanomaterials to form novel nanocomposites for a variety of potential applications. We present an approach for the in situ preparation of graphene–zinc oxide nanocomposites through a reflux process in which either zinc acetate or zinc chloride can serve as precursors. The synthesized samples were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray analysis, ultraviolet–visible spectroscopy and thermogravimetry analysis (TGA–DSC) for structural, optical and thermal properties. It has been found that nanocomposites comprise of zinc oxide (ZnO) nanostructures deposited on graphene sheets, and the choice of zinc precursor has a deterministic influence on the morphology, structure and properties of the graphene–ZnO nanocomposites. In addition, the novel structure of zinc acetate based nanocomposite has induced improved absorption and thermal stability of the graphene/ZnO nanocomposite as compared to zinc chloride based nanocomposite and would be promising for future applications in nanotechnology.     

Structure and Optical Properties of Chalcogenide Glassy As–Ge–Te Semiconductor

Semiconductors - The structure and optical properties of a chalcogenide glassy As–Ge–Te semiconductor film are studied by X-ray diffraction analysis, Raman spectroscopy, and optical...     

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloys

利用显微光致发光技术,观测到了N含量为0.1%,0.22%,0.36%和0.62%的GaAsN合金的E0,E0 △0和E 能级的光致发光峰.共振喇曼散射谱进一步证实了这些发光峰来源于所研究材料的本征能级,而不是来源于GaAsN合金中的一些局域激子发射.随着N组分的增加,E0 △0和E 能级分别向低能和高能方向移动并在N组分为0.16%时发生交错.文中提出了一种少量等电子掺杂和显微光致发光谱相结合的方法来直接观测半导体材料带边以上的跃迁能级,尽管光致发光谱通常没有用来观测这些能级位置.     

Pure-Cubic Optical Soliton Perturbation with Complex Ginzburg–Landau Equation Having a Dozen Nonlinear Refractive Index Structures

Journal of Communications Technology and Electronics - This paper recovers soliton solutions to perturbed pure–cubic complex Ginzburg–Landau equation having a dozen forms of nonlinear...     

ESD sensitivity of AlGaAs and InGaAsP based Fabry–Perot laser diodes

The sensitivity to electrostatic discharges of Fabry–Perot laser diodes with InGaAsP as active layer material has been tested and compared to Fabry–Perot lasers based on AlGaAs as active layer material. In the case of the forward-bias ESD pulses we observed a substantially lower degradation threshold voltage for the AlGaAs type lasers as compared to the InGaAsP type lasers. A detailed analysis of the optical and electrical parameters before and after ESD test with particular emphasis on the characteristic temperature and optical emission spectra changes has been done. Effective suppression of the optical emission on a ns-time scale due to device heating during the forward-bias ESD pulses has been evidenced by monitoring the light emission during ESD pulses.     

Design and Implementation of a Bandpass–Bandpass Diplexer Using Coupled Structures

Wireless Personal Communications - In this paper, a bandpass–bandpass two channels diplexer with operating frequencies of 1.7 GHz and 2.1 GHz is designed and fabricated on RT/duroid...     

Optical and morphological properties of InGaAs/AlGaAs self-assembled quantum dot nanostructures for 980 nm room temperature emission

This work deals with the study of optical and morphological properties of InGaAs/AlGaAs quantum dot(QD) structures grown by molecular beam epitaxy(MBE) . Photoluminescence(PL) emission energies,activation energies of PL quenching and QD sizes are studied as functions of the Al content in the AlyGa1-yAs confining layers(CL) . We show that the PL emission energy of In(Ga) As/AlyGa1-yAs QD structures increases with increasing y and that the sizes of InAs/AlyGa1-yAs QDs decrease with increasing y. By the comparison of the experimental results with those of an effective-mass model developed to calculate the QD fundamental transition energies,we show that the blueshift of emission energy has to be ascribed not only to the increase in barrier discontinuities that confine the carriers into QDs but even to effects related to changes of the QD morphology dependent on CL composition. Moreover,we show that the Al content in the barriers determines also the activation energy of thermal quenching of PL,which depends on the thermal escape of carriers from QD levels. These studies resulted in the preparation of structures with efficient light-emission in the 980 nm spectral window of interest for lightwave communications.     

Compact Blocking 8×8 Optical Matrix Switch on S01 with Taper Waveguides and Self-Aligned Total Internal Reflection Mirrors

Novel folding 8×8 matrix switches based on silicon.on-insulator(SOI)were demonstrated.In the design,single mode rib waveguides and multimode interferences(MMIs)are connected by optimized tapered waveguides to reduce the mode coupling loss between the two types of waveguides.And the self-aligned method was applied to the key integrated turn· ing mirrors for perfect positioas and low loss of them.The switch element( SE) with high switching speed and low power consumption is presented in the matrix.The average insertion loss of the matrix is about 21dB and the excess loss of one mir· rot is measured to be 1.4dB.The worst crosstalk is larger than -21dB.Experimental results show that some of the main characteristics of optical matrix switches are developed in the modified design,which agree with the theoretieal analyses.     

Structure and Optical Properties of Chalcogenide Glassy Semiconductors of the As–Ge–Se System

Semiconductors - The types of structural elements and chemical bonds forming an amorphous matrix of chalcogenide glassy semiconductors of the As–Ge–Se system and changes occurring in...     

Specific Features of Carrier Transport in n+–n0–n+ Structures with a GaAs/AlGaAs Heterojunction at Ultrahigh Current Densities

Semiconductors - The current–voltage characteristics of n+-GaAs/n0-GaAs/N0-AlGaAs/N+-AlGaAs/n+-GaAs isotype heterostructures and n+-GaAs/n0-GaAs/n+-GaAs homostructures are studied. It is...     

A New Nonlinear Optically Active Donor–Acceptor-Type Conjugated Polymer: Synthesis and Electrochemical and Optical Characterization

A new donor–acceptor-type poly[3-{5-[3,4-didodecyloxy-5-(1,3,4-oxadiazol- 2-yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}-9-dodecyl-9H-carbazole] (P) has been synthesized through multistep reactions. The new polymer P exhibited good thermal stability and film-forming behavior. The electrochemical band gap is estimated to be 2.15 eV. The polymer emits intense green fluorescence in the solid state. Third-order nonlinear optical (NLO) studies showed that the strong absorptive nonlinearity observed for the polymer is of the optical limiting type, which is due to an “effective” three-photon absorption (3PA) process. This 3PA process can have potential applications in photonic devices. The studies revealed that the new polymer P is a promising material for development of efficient optoelectronic devices.     

Optical and electronic interaction at metal–organic and organic–organic interfaces of ultra-thin layers of PTCDA and SnPc on noble metal surfaces

We investigate the interaction mechanisms at metal–organic and organic–organic interfaces in highly-ordered ultra-thin layers of the dye molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and tin(II)-phthalocyanine (SnPc) on single crystalline noble metals. The ultra-thin films are characterized by means of in situ differential reflectance spectroscopy (DRS), followed by an extraction of the optical functions by application of a numerical algorithm. For the first time, DRS data of PTCDA and SnPc films on Ag(1 1 1) are presented. We found that for the contact layers of PTCDA and SnPc the well-known covalent interaction between adsorbate and substrate is manifested in broad and structureless absorption spectra. Surprisingly, the optical spectra of the respective first monolayers on Ag(1 1 1) are almost identical despite of the rather different electronic structure of the free molecules. The special character of the optical spectra is emphasized by a comparison with PTCDA and SnPc monolayers on Au(1 1 1) where the electronic interaction at the metal–organic interface is much weaker. Quite differently from the contact layer, the second layer of the same molecule on Ag(1 1 1) clearly shows monomeric behavior which can only be observed if the electronic and optical coupling with the surrounding molecules and the substrate is faint. However, a very weak out-of-plane electronic interaction remains as concluded from the comparison with the spectra obtained on inert mica substrates. We also present structural data acquired with low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) of SnPc on Au(1 1 1).