Hot electron light-emitting semiconductor heterostructure device--type 2

A novel hot electron light-emitting device is proposed which operates by the application of longitudinal electric field, i.e. in the plane of the GaAs quantum wells, which are placed next to the junction plane of an n-Ga_1-xAl_xAs--p-GaAs heterostructure. Application of high electric fields results in the transfer of hot electrons via tunnelling and thermionic emission, from the quantum well in the depletion region, into the GaAs inversion layer. The hot holes in the p-GaAs, initially away from the junction, then diffuse towards the junction plane to recombine with the excess hot electrons, giving rise to electroluminescence (EL) which is representative of the GaAs band-to-band emission. As the applied field is increased, a high-energy tail in the EL spectrum develops, and, photons with energies greater than the el-hhl transition energy in the quantum well are absorbed and re-emitted by the quantum well. Thus a second peak develops in the EL spectra which becomes stronger with increasing applied electric field. The device has been theoretically modelled, by solving Schrodinger and Poisson's equations self-consistently, to understand the processes leading to EL emission in the various channels.     

Hot electron light-emitting and lasing semiconductor heterostructures--type 1

A new light-emitting device has been proposed based on the incorporation of a GaAs quantum well on the n-side, and in the depletion region, of a Ga_1-xAl_xAs p-n junction, where the bias is applied parallel to the layers. Light is emitted when electrons and holes on the n- and p-side of the structure, respectively, heated by the applied longitudinal electric field, transfer to the quantum well, by resonant tunnelling and thermionic emission (electrons) and diffusion (holes), where they recombine radiatively. The intensity of the light emitted is independent of the polarity of the applied bias. A demonstration of the device is presented and it is shown that the quantum well needs to be in the depletion region for light emission to occur. The device is modelled theoretically by solving the Schrödinger's and Poisson's equations self-consistently by including the carrier dynamics for hot electrons and holes.     

Tunable wavelength light emission from longitudinally biased p-GaAs/n-Ga1−xAlxAs junction containing GaAs quantum wells: non-linear dynamics

We report on the operation and non-linear dynamics of a hot electron device that emits light with wavelength tunablity. The device consists of p-GaAs/n-Ga_1−xAl_xAs heterojunction containing an inversion layer on the p-side, and GaAs quantum wells on the n-side. It is referred to as HELLISH-2 (Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure – Type 2). The device utilises hot electron longitudinal transport and the light emission is independent of the polarity of applied voltage. The wavelength of the emitted light can be tuned with applied bias from 1.50 to 1.61 eV. The operation of the device requires only two diffused in point contacts. Theoretical modelling of the device operation has been carried out and compared with the experimental results.     

沟槽型发射极SiGe异质结双极化晶体管新结构研究

提出了一种沟槽型发射极SiGe异质结双极化晶体管新结构. 详细分析了新结构中沟槽型发射极的引入对器件性能的影响,并对其机理进行研究. 新型发射极结构通过改变发射极电流路径使电阻分区并联,在不增大结电容的前提下,有效减小发射极电阻,提高器件的频率特性. 结果表明,新结构器件的截止频率和最大振荡频率分别增加至100.2 GHz和134.4 GHz,更重要的是沟槽型发射极结构的引入,在提高器件频率特性的同时,不会降低器件的电流增益,也不会增加结电容,很好实现了频率特性、电流增益和结电容之间的折中. 对沟槽型发射极进行优化设计,改变侧墙高度和侧墙宽度. 沟槽型发射极电阻不受侧墙高度改变的影响,频率性能不变;侧墙宽度增加,频率性能降低. 关键词： SiGe 异质结双极化晶体管 沟槽型发射极 发射极电阻     

Control of the Interface Between Electron‐Hole and Electron‐Ion Plasmas: Hybrid Semiconductor‐Gas Phase Devices as a Gateway for Plasma Science

Coupling electron‐hole (e^–‐ h⁺) and electron‐ion plasmas across a narrow potential barrier with a strong electric field provides an interface between the two plasma genres and a pathway to electronic and photonic device functionality. The magnitude of the electric field present in the sheath of a low temperature, nonequilibrium microplasma is sufficient to influence the band structure of a semiconductor region in immediate proximity to the solid‐gas phase interface. Optoelectronic devices demonstrated by leveraging this interaction are described here. A hybrid microplasma/semiconductor photodetector, having a Si cathode in the form of an inverted square pyramid encompassing a neon microplasma, exhibits a photosensitivity in the ～420–1100 nm region as high as 3.5 A/W. Direct tunneling of electrons into the collector and the Auger neutralization of ions arriving at the Si surface appear to be facilitated by an n ‐type inversion layer at the cathode surface resulting from bandbending by the microplasma sheath electric field. Recently, an npn plasma bipolar junction transistor (PBJT), in which a low temperature plasma serves as the collector in an otherwise Si device, has also been demonstrated. Having a measured small signal current gain h_fe as large as 10, this phototransistor is capable of modulat‐ing and extinguishing the collector plasma with emitter‐base bias voltages <1 V. Electrons injected into the base when the emitter‐base junction is forward‐biased serve primarily to replace conduction band electrons lost to the collector plasma by secondary emission and ion‐enhanced field emission in which ions arriving at the base‐collector junction deform the electrostatic potential near the base surface, narrowing the potential barrier and thereby facilitating the tunneling of electrons into the collector. Of greatest significance, therefore, are the implications of active, plasma/solid state interfaces as a new frontier for plasma science. Specifically, the PBJT provides the first opportunity to control the electronic properties of a material at the boundary of, and interacting with, a plasma. By specifying the relative number densities of free (conduction band) and bound (valence band) electrons at the base‐collector interface, the PBJT's emitter‐base junction is able to dictate the rates of secondary electron emission (including Auger neutralization) at the semiconductor‐plasma interface, thereby offering the ability to vary at will the effective secondary electron emission coefficient for the base surface (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantum-dot superluminescent diode: A proposal for an ultra-wide output spectrum

We propose a novel superluminescent diode (SLD) with a quantum dot (QD) active layer, which should give a wider output spectrum than a conventional quantum well SLD. The device makes use of inhomogeneous broadness of gain spectrum resulting from size inhomogeneity of self-assembled quantum dots grown by Stranski– Krastanow mode. Taking a design made out in the In_xGa_1-xAs/GaAs system for example, the spectrum characteristics of the device are simulated realistically, 100–200 nm full width of half maximum of output spectrum can be obtained. The dependence of the output spectrum on In composition, size distribution and injection current of the dots active region is also elaborated.     

Regulated and entangled photons from a single quantum Dot

We propose a new method of generating nonclassical optical field states. The method uses a semiconductor device, which consists of a single quantum dot as active medium embedded in a p- i- n junction and surrounded by a microcavity. Resonant tunneling of electrons and holes into the quantum dot ground states, together with the Pauli exclusion principle, produce regulated single photons or regulated pairs of photons. We propose that this device also has the unique potential to generate pairs of entangled photons at a well-defined repetition rate.     

intersubband pumping of an : InP symmetric double quantum well terahertz laser

The feasibility of intersubband optical excitation of a terahertz (1–10 THz) or far-infrared (30–300 ) emitter/laser by a laser diode is investigated by means of envelope function/effective mass approximation and subband carrier lifetime calculations. The material system is employed in order to supply the necessary conduction band offset and the basic design is that of a 6-level symmetric double quantum well. This can simultaneously satisfy the criteria of an 800 meV intersubband absorption and a far-infrared emission. It is shown that these device designs can satisfy a necessary criterion for population inversion at room temperature. A scheme for improving the population ratio based on a 9-level triple quantum well is discussed.     

MgO衬底上YBa2Cu3O7-δ台阶边沿型约瑟夫森结的制备及特性

MgO衬底上的YBa2Cu3O7-δ(YBCO)台阶边沿型约瑟夫森结(台阶结)在高灵敏度高温超导量子干涉器(superconducting quantum interference device,SQUID)等超导器件研制方面具有重要的应用价值和前景.本文对此类YBCO台阶结的制备和特性进行了研究.首先利用离子束刻蚀技术和两步刻蚀法在MgO(100)衬底上制备陡度合适、边沿整齐的台阶,然后利用脉冲激光沉积法在衬底上生长YBCO超导薄膜,进而利用紫外光刻制备出YBCO台阶结.在结样品的电阻-温度转变曲线中,观测到低于超导转变温度时的电阻拖尾现象,与约瑟夫森结的热激活相位滑移理论一致.伏安特性曲线测量表明结的行为符合电阻分路结模型,在超导转变温度TC附近结的约瑟夫森临界电流密度TC随温度T呈现出(TC-T)^2的变化规律,77 K时JC值为1.4×10^5 A/cm^2.利用制备的台阶结,初步制备了YBCO射频高温超导SQUID,器件测试观察到良好的三角波电压调制曲线,温度77 K、频率1 kHz时的磁通噪声为250μΦ0/Hz^1/2.本文结果为进一步利用MgO衬底YBCO台阶结研制高性能的高温超导SQUID等超导器件奠定了基础.     

Buried emitter solar cell structures: Decoupling of metallisation geometry and carrier collection geometry of back contacted solar cells

We present a novel solar cell structure, the “buried emitter solar cell”. This concept is designed for decoupling the metallisation geometry from the geometry of the carrier collecting p–n junction in back‐contacted (and in particular back‐junction) solar cells without requiring electrical insulation by dielectric layers. The most prominent features of this device structure are a carrier collecting emitter that covers close to 100% of the total cell area and an effective electrical insulation between emitter and base metallisation via a p⁺–n⁺ junction. The experimental results presented in this paper report a 19.5% efficient “buried emitter solar cell”, where 50% of the solar cell's rear side exhibit a p⁺–n⁺ junction. This preparation technique implies covering a boron‐doped p‐type emitter with an n‐type surface layer that can be efficiently surface‐passivated by thermal oxidation. All structuring of this cell has been performed by laser processing without any photo‐lithography. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nano-plasmon enhancement effect on MWIR light emitting diode performance

We observed a significant increase in electro luminescence from GaSb based mid-wave infrared (MWIR) LED device through coupling with localized surface plasmon of a single layer Au nano-particles. We fabricated an interband cascade (IC) LED device with nine cascade active/injection layers with InAs/Ga_1−x In_xSb/InAs quantum well (QW) active region. Thin Au plasmon layer of 20 nm thickness is deposited on top anode electrode by e-beam technique, which resulted in 100% increase in light output for 50 μm square mesa device. We also observed a reduction in the device turn on voltage and increase in the apparent black body emission temperature due to nano-structure surface plasmon layer.     

太赫兹量子阱光电探测器光栅耦合的模拟与优化

光栅耦合是量子阱光电探测器探测正入射电磁辐射的常用耦合方法,本文采用模式展开法研究了一维金属光栅太赫兹量子阱光电探测器中的电磁场分布,并给出了器件有源区中的平均光强.研究结果表明,若一维光栅的周期与太赫兹波在器件材料中的波长相当,并且根据器件结构选取合理的光栅占空比,可使器件中的平均光场最强,光栅的光耦合效率最高,从而提高器件的响应率. 关键词： 太赫兹 量子阱光电探测器 光栅     

Dark currents of GaAs/AlGaAs quantum-well infrared photodetectors

We study the dark current of the GaAs/AlGaAs quantum-well infrared photodetector (QWIP) by assuming a drift-diffusion carrier transport in the barriers where the electric fields are obtained by the current continuity condition and the self-consistent energy band structure. It has been shown that due to the current continuity condition, the dark currents across the QWIP devices are determined by the thermionic emission from the emitter to the multiple quantum well (MQW) region. The self-consistent calculation of the Schrödinger and Poisson equations shows a weak electric field in the barrier region connecting to the emitter (much smaller than the average field across the QWIP at low bias) due to the accumulation of carriers in the triangle quantum well formed at the emitter-MQW interface, which results in a very small dark current at low bias. The numerical results explain well our experimental observation.     

Hardening measures for bipolar transistors against microwave-induced damage

In the present paper we study the influences of the bias voltage and the external components on the damage progress of a bipolar transistor induced by high-power microwaves. The mechanism is presented by analyzing the variation in the internal distribution of the temperature in the device. The findings show that the device becomes less vulnerable to damage with an increase in bias voltage. Both the series diode at the base and the relatively low series resistance at the emitter, Re, can obviously prolong the burnout time of the device. However, Re will aid damage to the device when the value is sufficiently high due to the fact that the highest hot spot shifts from the base-emitter junction to the base region. Moreover, the series resistance at the base Rb will weaken the capability of the device to withstand microwave damage.     

新型宽温区高热稳定性微波功率SiGe 异质结双极晶体管

宽温区大电流下的热不稳定性严重制约着功率SiGe 异质结双极晶体管 (HBT) 在射频和微波电路中的应用.为改善器件的热不稳定性, 本文利用SILVACO TCAD建立的多指功率SiGe HBT模型, 分析了器件纵向结构中基区Ge组分分布对微波功率SiGe HBT电学特性和热学特性的影响. 研究表明, 对于基区Ge组分为阶梯分布的HBT, 由于Ge组分缓变引入了少子加速电场, 使它与均匀基区Ge组分HBT相比, 具有更高的特征频率f_T, 且电流增益β和f_T随温度变化变弱, 这有利于防止器件在宽温区工作时电学特性的漂移.同时, 器件整体温度有所降低, 但器件各指温度分布均匀性较差.考虑多指HBT各发射极指散热能力存在差异, 在器件纵向结构设计为基区Ge组分阶梯分布的同时, 对其横向版图进行发射极指间距渐变结构设计, 用于改善器件各指温度分布的均匀性, 进而提高HBT的热稳定性.结果表明, 与基区Ge组分为均匀分布的等发射极指间距结构HBT相比, 新器件各指温度分布均匀性明显改善, f_T保持了较高的值, 且β和f_T 随温度变化不敏感, 热不稳定性得到显著改善, 显示了新器件在宽温区大电流下工作的优越性. 关键词： SiGe 异质结双极晶体管 Ge组分分布 发射极指间距渐变技术 热稳定性     

The role of emitter quasi-bound state and scattering on intrinsic bistability in resonant tunneling diodes

Usually, numerical self-consistent calculations predict a much larger intrinsic bistability region than actually is measured in resonant tunneling diodes (RTDs). In addition, numerical calculations have shown that scattering in the well reduces bistability. We used a unified treatment of current flowing from continuum states and emitter quasi-bound states to show numerically and analytically that not only the scattering in the quantum well but also the scattering in the emitter reduces bistability. Moreover, within the Hartree approximation, bistability occurs by tunneling resonantly between emitter quasi-bound state and well quasi-bound state as a pitchfork bifurcation.     

Nondoped phosphorescent organic quantum well light-emitting device based on iridium complex: Synthesis, characterization, photophysical property, and electroluminescence performance

In this paper, we report a phosphorescent Ir(III) emitter of Ir(acac)(F-BT)₂, where acac=acetylacetonate and F-BT=2-(2-fluorophenyl)benzo[d]thiazole, including its crystal structure, electronic nature, photophysical characteristics, thermal, and electrochemical properties. Data suggest that Ir(acac)(F-BT)₂ is a promising emitter with high quantum yield of 0.61 and good thermal stability, along with its proper energy levels for charge carrier transportation. Multiple quantum well (MQW) structured OLEDs using Ir(acac)(F-BT)₂ as emitter are also fabricated, and their electroluminescence (EL) are investigated in detail. The optimal EL device with 4,4′-N,N′-dicarbazole-biphenyl as potential well layer shows a maximum luminance of 85,500 cd/cm² and a peak current efficiency of 31.5 cd/A, and the efficiency roll-off is efficiently reduced.     

Threshold, power, and spectral characteristics of a semiconductor emitter with a fiber Bragg grating

The threshold, power, and spectral characteristics of an emitter with a fiber Bragg grating are calculated. The effect of heating of the active region of a laser diode, its thermal resistance, and radiation power extracted from the cavity of the emitter on these characteristics is investigated. It is shown that satisfactory agreement between the theory and experiment is observed when the heating of the active zone of the laser diode by the pump current flowing through it and the radiation power extracted from the cavity of the emitter are taken into account.     

双外延基区4H-SiC BJTs的建模与仿真

基于4H-SiC的材料特性,对具有双外延基区结构的4H-SiC双极晶体管进行研究.通过分析该结构在基区内部形成的自建电场以及基区渡越时间,利用正交试验的方法,基于各种器件二维模型,对该器件结构进行数值计算,并进行平均极差分析.计算结果表明,该器件的共发射结电流增益最高可达72,具有负温度系数,并且在一个很宽的集电极电流范围内该特性保持不变.     

Scanned probe imaging of nanoscale conducting channels in Pt/alkanoic acid monolayer/Ti devices

The mechanisms responsible for switching in metal/molecule/metal systems are subjects of intense research. We report here a scanned probe technique that maps the conductance of a planar molecular junction (Pt/stearic acid monolayer/Ti) under mechanical perturbation by using an atomic force microscope (AFM) to apply a localized force to a molecular junction while measuring the junction conductance. Such mechano-conductance maps reveal that transport through the molecular device is dominated by nanoscale conducting channels, which emerged or disappeared when the junction is switched into higher or lower conductance states. A quantitative model that combines quantum tunneling with the growth of nano-asperities effectively describes the experimental conductance data across a wide range of device conductance. PACS 68.37.Ps; 73.23.-b; 73.63.-b; 81.07.Pr; 85.65.+h