Microplasma effects in gallium arsenide epilayers and FETs

Breakdown of GaAs field-effect transistor (FET) structures is primarily a substrate effect beginning near the positive ohmic contact. The electric field across the space charge layer of the diode between the active layer and the surface of the substrate can exceed the avalanche breakdown value. The avalanche process is active at higher drain voltages, though still far from the burnout voltage. Microplasma effects were observed in addition to light emission and high noise power generation in gated and ungated FETs. The microplasma ignition should be originated from electron trapping in the epi-substrate interface. The back-side gating mechanism diminishes entirely in the avalanche breakdown region. Gunn oscillations were also observed but only in pulsed bias conditions.     

Quantum phenomena in field-effect-controlled semiconductornanostructures

Quantum effects resulting from sub-100 nm features in planar, field-effect-controlled semiconductor structures or devices are discussed, and experimental results are compared with calculations. These devices are based on the GaAs-AlGaAs modulation-doped field-effect transistor (MODFET) and include grating-gate lateral surface superlattices. (LSSLs), grid-gate LSSLs, planar-resonant-tunneling field-effect transistors (PRESTFETs), multiple parallel quantum wires (MPQWs), and arrays of quantum dots (QDs). In contrast to conventional, epitaxially grown vertical quantum structures, planar structures offer the opportunity for electron confinement in three, two, and one dimensions and the flexibility of electrical tuning of quantum effects     

GaAs:GaAlAs ridge waveguide lasers and their monolithic integrationusing the ion beam etching process

The fabrication and performance characteristics of GaAs/GaAlAs ridge waveguide lasers are discussed. Threshold currents as low as 8 mA and differential quantum efficiencies as high as 90% were obtained for 250-μm-long graded-index separate-confinement heterostructure with single quantum well (GRINSCH SQW) lasers. High-speed short-cavity ridge waveguide lasers for which both the ridge stripe and one-mirror facet were formed by Ar-ion beam etching were achieved. The dependence of threshold current and lasing spectra on the cavity length were theoretically and experimentally investigated. This process was successfully used to integrate a laser diode monolithically with a photodiode or a field-effect transistor     

Planar FET oscillators using periodic microstrip patch antennas

An integrated oscillator/antenna is presented that uses a single microstrip leaky-wave structure as both the resonant and the radiating element. This resonant antenna is connected to a GaAs metal-semiconductor field-effect transistor which acts as the negative resistance element in the oscillator circuit. This type of oscillator is similar in its operating principle to one reported using Gunn diodes and a periodically notched dielectric image guide. This circuit exhibits the high DC-RF conversion efficiency that is typical of field-effect transistor oscillators. The planar circuit is simple and inexpensive to construct, occupies a small volume, and can conform to different surface profiles. Such circuits are suitable for use in millimeter-wave systems as well as at microwave frequencies. A design procedure is given, and the performance of X-band prototype circuits is reported. Prototype circuits showed a 9 dB isotropic conversion gain and 40 MHz tuning range at 9.5 GHz     

Transistor performance and electron transport properties of highperformance InAs quantum-well FET's

A novel field-effect transistor based on a pseudomorphic InAs quantum well in a doped InGaAs/InAlAs double heterostructure is reported. Low-field mobility, electron peak velocity, and transistor performance are studied as functions of InAs quantum well thickness, where the InAs layer is in the center of a 300-Å uniformly doped InGaAs/InAlAs quantum well lattice matched to InP. Electron transport-both at low and high fields-along with transistor transconductance are optimal for structures with a 30-Å InAs quantum well. Transistors based on the InAs quantum well structures with 0.5-μm gate lengths yielded room temperature extrinsic transconductances of 708 mS/mm, more than a 100% increase over those with no InAs     

Study of the Harmonic Effects for Waveguide Gunn-Diode Oscillator Optimization

The dependence on harmonic load conditions of waveguide Gunn oscillator performance is theoretically and experimentally studied. A simple waveguide mount is presented, which by controlling the diode harmonic load conditions, with one single adjustment permits considerable simultaneous improvement in output power, bias tuning, and varactor tuning linearities, as well as in frequency stability with the temperature. The oscillator noise level can also be minimized, though not at the same time as the other improvements. Finally, the usefulness of harmonic control in simplifying some typical thermal procedures is shown.     

Optimization and Realization of Planar Isolated GaAs Zero-Biased Planar Doped Barrier Diodes for Microwave/Millimeter-Wave Power Detectors/Sensors

A high tangential signal sensitivity (TSS) zero-bias GaAs planar doped barrier (PDB) diode for microwave and millimeter-wave power detection applications is presented. The fabricated PDB diodes have shown 4 dB better TSS at 35 GHz than that of reported devices, considerably increasing the minimum detectable power and widening the dynamic range. The high TSS was obtained by optimizing the PDB layer structures, namely, the delta-doped p⁺⁺ layer and the two intrinsic layers, and by employing ion bombardment to better define the device and reduce parasitic effects. The isolation properties of ion bombarded epitaxial layers on GaAs substrates were examined and optimized to have a sheet resistivity of 10⁸ Omega/sq. The temperature dependence of the barrier height of the PDB diode has been investigated experimentally, showing positive temperature coefficient and, hence, better thermal stability. We have also defined the critical barrier height and derived its analytical expression, which gives the theoretically lowest possible barrier height of a PDB diode     

Design and Performance of X-Band Oscillators with GaAs Schottky-Gate Field-Effect Transistors

The circuit construction and design of an X-band oscillator with a GaAs Schottky-gate FET have been studied. The oscillation characteristics including stability and noise performance have been examined in order to clarify the position of a GaAs FET as a microwave solid-state oscillator device. The experiments have revealed that 1) the GaAs FET simultaneously possesses the most desirable features of both Gunn and IMPATT oscillators, i.e., low bias voltage operation and fairly high efficiency, and 2) it is situated between Gunn and GaAs IMPATT oscillators with respect to noise properties. The results indicate that the GaAs FET oscillator will soon be joining the family of microwave solid-state oscillators as a promising new member.     

Nonlinear response and nonlinear coherent generation in resonant-tunneling diode in a broad frequency range

Nonlinear response and coherent generation in a resonant-tunneling diode within a broad range of frequencies and field amplitudes are theoretically studied for real structures under dc bias voltage. The results are shown to be in a good qualitative agreement with the idealized model if the widths of the resonance level Γ are identical for both quantum wells. Thus, the generation of high-power terahertz-frequency fields within the quantum mode is possible under real conditions. It is explicitly shown that the transient time of current in resonant-tunneling diodes is equal to the reciprocal of Γ.     

超宽禁带半导体Ga2O3微电子学研究进展

半导体材料Ga2O3是继宽禁带半导体材料SiC/GaN之后新兴的直接带隙超宽禁带氧化物半导体,其禁带宽度为4.5~4.9eV,击穿电场强度高达8MV/cm(是SiC及GaN的2倍以上),物理化学稳定性高,在发展下一代电力电子学和固态微波功率电子学领域具有较大的潜力。自2012年第一只Ga2O3场效应晶体管诞生以来,Ga2O3微电子学的研究呈现快速发展态势。本文综述了β-Ga2O3单晶材料和外延生长技术以及β-Ga2O3二极管和β-Ga2O3场效应管等方面的研究进展,介绍了β-Ga2O3材料和器件的新工艺、新器件结构以及性能测试结果,分析了相关技术难点和创新思路,展望了Ga2O3微电子学未来的发展趋势。     

Analysis of the formation of structures and chaotic dynamics in a nonrelativistic electron beam with a virtual cathode in the presence of a decelerating field

A nonrelativistic electron beam with a virtual cathode situated in the diode gap with a decelerating field is experimentally and theoretically studied. A 1D model of the electron beam in the presence of a decelerating field is constructed. Nonlinear nonstationary processes in this system are investigated by means of numerical analysis of the model. The processes are described and interpreted with regard to formation and interaction of structures in the electron flow. The theoretical results are qualitatively confirmed by the experimental data showing that the system under study can be considered as a promising controlled source of chaotic oscillations in the microwave range.     

Two-dimensional domain dynamics in a planar Schottky-gate Gunn-effect device

A two-dimensional computer-aided analysis on the domain dynamics in a planar Gunn device with a Schottky-barrier gate has been performed both for the repeatedly nucleated-domain mode (continuous operation) and for the triggered single-domain mode (triggered operation). The difference in the domain behavior between planar devices with coplanar ohmic electrodes and with parallel ohmic electrodes leads to a conclusion that the edge effect caused by the current crowding at the anode deteriorates the switching speed associated with the domain formation and extinction on the planar Gunn device with the coplanar electrodes. It is shown how a domain is nucleated under the gate, travels to the anode, and disappears there in the presence of the two-dimensional effects. The mechanism of the Schottky-gate triggering on the reverse-biased condition which differs substantially from the FET model has been made clear.     

InAlAs/InGaAs调制掺杂场效应晶体管研究

从理论上和实验上对InAlAs/InGaAs调制掺杂场效应晶体管(MODFET)进行了研究。建立了简单的一维电荷控制模型,并进行二维数值模拟,得到了不同偏压下器件内部电势分布和电子浓度分布。在上述理论的指导下,设计了我们所需要的器件纵向和横向结构,并对设计器件的直流特性进行了计算机辅助分析。最后叙述了利用国产Ⅳ型MBE设备生长的材料制作出MODFET的工艺过程,并对器件的直流特性和射频特性进行了测试和分析。直流测试表明,器件的最大饱和电流密度为125mA/mm,最大非本征跨导达250mS/mm;射频测试得到器件(L_g=1.0～1.2βm,W_g=150μm)的特征频率f_T为26GHz,最高振荡频率f_(max)为43GHz。     

Modulation of absorption in field-effect quantum well structures

Experimental and theoretical investigations of the absorption in a single-modulation-doped quantum well (QW) used as conducting channel of a field-effect transistor are presented. By applying a voltage to the gate, the electron concentration can be varied between 0 and ~10¹² cm^-2. The continuous transition can be optically followed from an undoped to a highly doped QW. Effects of band filling are observed, along with renormalized effects at the first subband edge and electrostatic effects at the higher ones. It is shown that optical techniques can give in situ information on the electron density and temperature as well as on the electrostatic fields inside field-effect structures     

Bistable switching in a planar Gunn diode

This paper presents experimental and theoretical results showing that bistable switching, due to an anode-triggered trapped domain (TD), can be realized in a Gunn diode with an anode notch. The characteristics of the anode-triggered TD have been made clear by computer simulations. Bistable switching has been confirmed experimentally by using a planar Gunn diode with a groove, which was intentionally dug close to the anode.     

Noise figure and conversion loss of self-excited Gunn-diode mixers

Gunn-effect oscillators, used as self-excited mixers in X band/v.h.f. band convertors, are investigated. Noise figure and conversion loss are measured. It is shown that both fairly high oscillator Q factor and proper matching of the input signal to the Gunn diode leads to mixers comparable in performance with usual microwave mixers. Because of the negative differential resistance of Gunn diodes, conversion gain is easily realisable.     

Ge-ZnSSe Spatial Wavefunction Switched (SWS) FETs to Implement Multibit SRAMs and Novel Quaternary Logic

This paper describes novel multibit static random-access memories (SRAMs) implemented using four-channel spatial wavefunction switched field-effect transistors (SWS FETs) with Ge quantum wells and ZnSSe barriers. A two-bit SRAM cell consists of two back-to-back connected four-channel SWS FETs, where each SWS FET serves as a quaternary inverter. This architecture results in a reduction of the field-effect transistor (FET) count by 75% and data interconnect density by 50%. The designed two-bit SRAM cell is simulated using Berkeley short-channel insulated-gate field-effect transistor equivalent-channel models (for 25-nm FETs). In addition, the binary interface logic and conversion circuitry are designed to integrate the SWS SRAM technology. Our motivation is to stack up multiple bits on a single SRAM cell without multiplying the transistor count. The concept of spatial wavefunction switching (SWS) in the FET structure has been verified experimentally for two- and four-well structures. Quantum simulations exhibiting SWS in four-well Ge SWS FET structures, using the ZnSe/ZnS/ZnMgS/ZnSe gate insulator, are presented. These structures offer higher contrast than Si-SiGe SWS FETs.     

Some effects of wave propagation in the gate of a microwave m.e.s.f.e.t.

In microwave field-effect transistors there is a progressive phase delay as a signal propagates along the gate, with a corresponding delay in channel modulation across the width of the transistor. It is shown that this leads to a phase lag in gm while the modulus of gm is comparatively unaffected.     

Plasma oscillations of the two-dimensional electron gas in the field-effect transistor with a cylindrical gate electrode

The frequency characteristics of the two-dimensional electron gas in the field-effect transistor with with a cylindrical gate electrode are obtained in the framework of the linear hydrodynamic model. The effect of the transverse dimension and the position of the gate electrode and the parameters of thetwo-dimensional electron gas layer on the resonance characteristics of the field-effect transistor is analyzed. The practical prospects of the results in the development of nanosized oscillators and detectors of the terahertz electromagnetic radiation are outlined.     

Effects of the operational modes on the temperature dependence of the Gunn diode admittance

the analytical expressions for the large-signal admittances of Gunn diodes including the temperature dependence have been derived theoretically for the quenched- and delayed-domain modes by using a piece-wise linear approximation for the velocity-field characteristic. As the main physical parameters affecting the temperature dependence of the Gunn diode admittance, the following have been considered; the domain transit time, the domain formation time, the domain extinction time, the low-field mobility and the dielectric constant. The analysis shows that the diode conductance decreases with increasing microwave voltage and temperature for both the quenched- and delayed-domain modes, whereas the dependence of the diode susceptance on the microwave voltage and temperature is different between the two modes. This difference is explained by the temperature dependence of the domain transit time, the domain formation time, and the low-field mobility. The variation of oscillation frequency due to the change of the diode admittance has also been discussed.