Ferrite devices and materials

The development and current status of microwave ferrite technology is reviewed in this paper. An introduction to the physics and fundamentals of key ferrite devices is provided, followed by a historical account of the development of ferrimagnetic spinel and garnet (YIG) materials. Key ferrite components, i.e., circulators and isolators, phase shifters, tunable filters, and nonlinear devices are also discussed separately     

SiC材料与器件

介绍了碳化硅材料和器件的最新进展     

Wide bandgap semiconductor materials and devices

Given a matrix of all semiconductor materials and their properties, the highest and the lowest of these property values will almost always be associated with wide bandgap materials. The many possible combinations of these “poles and zeros” lead not only to superlative electron device performance, but to new device concepts as well. An overview of wide bandgap semiconductor properties is presented followed by several concepts for both new and enhanced devices. Finally, impediments to immediate exploitation and a time-oriented appraisal of the various materials and devices is presented     

Oxide thin-film electroluminescent devices and materials

This report reviews newly developed oxide phosphors shown to be promising as the emitting layer of thin-film electroluminescent (TFEL) devices. Since the first report of a high-luminance TFEL device using a Mn-activated Zn₂SiO₄ (Zn₂SiO₄:Mn) phosphor, high-luminance multicolor-emitting TFEL devices have been fabricated using various oxide phosphors activated with Eu or Mn. In addition, many oxides that consist of binary and ternary compounds and multicomponent oxides have been developed and shown to be promising as a host material for TFEL phosphors. This report focuses on Mn-activated Y₂O₃-based oxide phosphors: a binary compound and various ternary compounds and multicomponent oxides, composed of Y₂O₃ in combination with another binary compound such as Ga₂O₃ or GeO₂. TFEL devices of which every constituent was an oxide material were fabricated using oxide phosphor thin films deposited by r.f. magnetron sputtering, pulsed laser deposition or a sol–gel process. High luminances and luminous efficiencies comparable to those of TFEL devices using ZnS:Mn sulfide phosphor were realized using Mn-activated Y₂O₃-based oxide phosphors. Luminances above 7000 cd/m² (1 kHz-driving voltage) and luminous efficiencies of approximately 10 lm/W (60 Hz driving voltage) were obtained in yellow emitting TFEL devices fabricated using a Y₂O₃:Mn, a ((Y₂O₃)_0.6–(GeO₂)_0.4):Mn or a ((Y₂O₃)_0.5–(Ga₂O₃)_0.5):Mn thin film and driven by an ac sinusoidal wave voltage. Also, a high luminance above 1000 cd/m² for green emission was obtained in a ((Y₂O₃)_0.3–(Ga₂O₃)_0.7):Mn TFEL device driven at 1 kHz.     

Progress in ZnO materials and devices

ZnO is a wide-band-gap semiconductor material that is now being developed for many applications, including ultraviolet (UV) light-emitting diodes, UV photodetectors, transparent thin-film transistors, and gas sensors. It can be grown as boules, as thin films, or as nanostructures of many types and shapes. However, as with any useful semiconductor material, its electrical and optical properties are controlled by impurities and defects. Here, we consider various important donor-type impurities, such as H, Al, Ga, and In, and acceptor-type impurities, such as N, P, As, and Sb. We also examine the effects of a few common point defects, including Zn interstitials, Zn vacancies, O vacancies, and complexes of each. The main experimental techniques of interest here include temperature-dependent Hall-effect and low-temperature photoluminescence measurements, because they alone can provide donor and acceptor concentrations and donor energies. The important topic of p-type ZnO is also considered in some detail.     

Ferroelectric ceramic electrooptic materials and devices

Thin polished plates of hot-pressed rhombohedral lead zirconate-lead titanate ceramics possess one of two types of electro-optic properties depending on the nominal grain diameter. In poled coarse-grained ceramics the electrooptic effect of importance for devices is the dependence of the light scattering properties on the orientation of the ceramic polar axis (electrical poling direction). The light scattering properties are essentially independent of the magnitude of electrical poling (ferroelectric remanence state). Poled fine-grained ceramics are birefringent, and their light transmission characteristics are similar to those of optically uniaxial crystals. These materials exhibit orthotropic symmetry with respect to the optic axis, which coincides with the ceramic polar axis. The fine-grained ceramic electrooptic effect of primary importance for devices is the dependence of the effective birefringence on the magnitude of electrical poling as well as on the intensity of the applied biasing electric field. Retardation of a ceramic plate can be varied incrementally by partial switching or continuously by application of a nonswitching bias field. Both coarse- and fine-grained ceramics have the property that localized areas as small as 25 µ by 25 µ can be poled or switched independently without affecting the light transmission characteristics of the surrounding area. The locally switched areas are stable with time, but they can be "erased" by switching them back to their original orientation. Each locally switched area can function as a light shutter, valve, or spectral filter depending on the ceramic material, the switching mode, and the characteristics of the incident light.     

Semiconductor materials for microwave devices

Microwave device performances have been rapidly improving due to recent developments in the areas of device construction and material preparation. In this paper emphasis is placed on material selection and preparation for several devices which are currently receiving attention throughout the industry. These include transferred electron devices, avalanche diodes, bipolar transistors, varactor and mixer diodes, and field effect transistors. The structures of these devices are considered with reference to the requirements which they place on the epitaxial layers. Various techniques of epitaxial growth are described together with the relative advantages and disadvantages of each.     

Organic materials for photovoltaic and light-emitting devices

Materials for organic photovoltaic cells and light-emitting devices are reviewed. Dye-sensitized systems represent the most studied of these materials as they offer high efficiency of photoelectric energy conversion. Systems demonstrating efficient luminescence were identified; they are based on conjugated polymers, complexes of rare-earth elements with organic ligands, and dyes. To achieve efficient photoelectric conversion, different types of sensitizing dyes will be tested. Phthalocyanines and pentacenes are of special interest. Phthalocyanines are the most promising materials: they are easily synthesized and nontoxic, and their electric characteristics are widely investigated. Harnessing the unique electron-acceptor properties of the C₆₀ molecule, one can attain considerable enhancement in the efficiency of solar-energy conversion into electricity. Organic photovoltaic cells are often made on the basis of aromatic and heterocyclic polymers—poly(p-phenylene-vinylene), polyanilines, polypyrroles, and polythiophenes. Organic photoconducting materials offer high photosensitivity and low dark current. They are readily available and can be easily deposited on a substrate, which make them suitable for the fabrication of relatively cheap photovoltaic cells.     

Dielectric materials, devices, and circuits

Dielectric materials are continuing to play a very important role in the microwave communication systems. These materials are key in realization of low-loss temperature-stable resonators and filters for satellite and broadcasting equipment, and in many other microwave devices. High dielectric-constant materials are critical to the miniaturization of wireless systems, both for the terminals and base-stations, as well as for handsets. In this paper, a sequential evolution of the dielectric materials applications in microwave devices will be reviewed. This includes dielectric waveguides, low-loss temperature-stable ceramic materials, dielectric resonators, and filters. The recent advances in the multilayer circuit modules, dielectric antennas, and ferroelectrics are also described     

Optoelectronic devices informatics: optimizing DSSC performance using random-forest machine learning algorithm

This paper provides an attempt to utilize machine learning algorithm, explicitly random-forest algorithm, to optimize the performance of dye sensitized solar cells (DSSCs) in terms of conversion efficiency. The optimization is implemented with respect to both the mesoporous TiO2 active layer thickness and porosity. Herein, the porosity impact is reflected to the model as a variation in the effective refractive index and dye absorption. Database set has been established using our data in the literature as well as numerical data extracted from our numerical model. The random-forest model is used for model regression, prediction, and optimization, reaching 99.87% accuracy. Perfect agreement with experimental data was observed, with 4.17% conversion efficiency.     

Theory of materials for thermoelectric and thermomagnetic devices

The relation between the thermoelectric figure of merit Z and the basic properties of the material such as carrier mobilities, band structure, thermal conductivity and minority carrier lifetime is discussed. For isotropic materials with parabolic bands it is shown that the figure of merit based on the Seebeck coefficient will increase when a magnetic field is applied, if acoustic-mode scattering is predominant. If optical-mode scattering is predominant, the figure of merit will increase if ZT>0.77. Materials for devices based upon the Nernst or Ettingshausen effects will have large figures of merit only if 1) (m^*)^3/2µ/κL is large, 2) the energy gap is less than kT, and 3) the electron and hole mobilities are similar. Materials requirements for Nernst- and Seebeck-type devices are compared.     

Ge-on-Si for Si-based integrated materials and photonic devices

This paper reviews the recent progress in photonic devices application of Ge-on-Si.Ge-on-Si materials and optical devices are suitable candidates for Si-based optoelectronic integration because of the ...     

Research progress of Si-based germanium materials and devices

Si-based germanium is considered to be a promising platform for the integration of electronic and photonic devices due to its high carrier mobility, good optical properties, and compatibility with Si CMOS technology. However, some great challenges have to be confronted, such as: (1) the nature of indirect band gap of Ge; (2) the epitaxy of dislocation-free Ge layers on Si substrate; and (3) the immature technology for Ge devices. The aim of this paper is to give a review of the recent progress made in the field of epitaxy and optical properties of Ge heterostructures on Si substrate, as well as some key technologies on Ge devices. High crystal quality Ge epilayers, as well as Ge/SiGe multiple quantum wells with high Ge content, were successfully grown on Si substrate with a low-temperature Ge buffer layer. A local Ge condensation technique was proposed to prepare germanium-on-insulator (GOI) materials with high tensile strain for enhanced Ge direct band photoluminescence. The advances in formation of Ge n⁺p shallow junctions and the modulation of Schottky barrier height of metal/Ge contacts were a significant progress in Ge technology. Finally, the progress of Si-based Ge light emitters, photodetectors, and MOSFETs was briefly introduced. These results show that Si-based Ge heterostructure materials are promising for use in the next-generation of integrated circuits and optoelectronic circuits.     

Microwave acoustic materials, devices, and applications

This paper surveys applications of acoustic waves in microwave devices. After a general and historical introduction to bulk acoustic waves (BAWs), surface acoustic waves (SAWs), practical wave types, and acoustoelectric transducers, a review is given of technologically important materials for microwave acoustic applications. Following this, we discuss BAW and SAW microwave devices and their technologies. Specifically reviewed are thin-film resonators and filters, transversal filters, and filters for correlative analog signal processing. Finally, an overview of the most important microwave applications is given, along with manufacturing and packaging issues     

Gallium-nitride-based materials for blue to ultravioletoptoelectronics devices

Breakthroughs in materials growth have enabled extremely high-efficiency blue and green GaN light emitting diodes (LEDs) to be achieved for the first time. Blue LEDs with external quantum efficiency exceeding 9% have enabled hybrid GaN/phosphor white lamp LEDs. GaN LEDs complete the primary color spectrum and have enabled bright and reliable full-color solid-state displays to be realized. Recently, room-temperature operation of continuous wave current-injection blue-violet lasers emitting at 417 nm has further increased the possible applications for GaN-based opto-electronic devices. In this paper, we review the key technologies for GaN-based materials and devices. Developments in the methods for thin-film deposition by metalorganic chemical vapor deposition and molecular beam epitaxy and resulting film properties are highlighted     

Recent advances in liquid crystal materials and display devices

This review article describes three recent areas of significant development in the field of liquid crystal materials and devices. In the first portion of the paper, an assessment is presented of the multiplexing performance of several materials used in twisted nematic displays. A novel concept of electronic temperature compensation is also mentioned. Next, the cholesteric nematic phase change with pleochroic dyes is discussed with primary emphasis on the liquid crystal materials. Finally, a new nonmultiplexed storage oscilloscope is described.