GaAs/AlGaAs electro-optic modulator with bandwidth >40 GHz

A high speed GaAs/AlGaAs travelling wave Mach-Zehnder electro-optic modulator has been fabricated. The device uses a novel slow wave electrode design to achieve phase velocity matching and has a measured electrical bandwidth >40 GHz     

A 3.3-V 21-Gb/s PRBS generator in AlGaAs/GaAs HBT technology

We present a pseudorandom bit sequence (PRBS) generator that outputs a 2⁷-1 bit pattern at rates up to 21 Gb/s. The circuit is implemented in a 40-GHz AlGaAs/GaAs heterojunction bipolar transistor (HBT) standard production process, operates from a single 3.3-V power supply, and consumes 1.1 W of power. We discuss variations of PRBS architecture and digital circuit topologies which exploit unique characteristics of AlGaAs/GaAs HBT devices. The work demonstrates the feasibility of using AlGaAs/GaAs HBT technology with low-voltage/low-power design techniques in complex high-speed circuits     

GaAs/AlGaAs多量子阱FET-SEED灵巧象元

将GaAs／AlGaAs多量子阱光探测器、光调制器与GaAs场效应晶体管（FET）混合集成,构成FET-SEED灵巧象元。光探测器和光调制器均为反射型自电光效应器件（SEED）,光源为骨子阱半导体激光器。测出的光输出Pout／光输入Pin特性表明,光输入信号对光输出信号有明显的调制作用,光输入信号较小的变化可以导致光输出信号较大的变化。     

All-optical photonic switches using integrated inverted asymmetricFabry-Perot modulators and heterojunction phototransistors

InGaAs/GaAs(100) multiple-quantum-well-based inverted cavity asymmetric Fabry-Perot modulators are vertically integrated with GaAs/AlGaAs heterojunction phototransistors to yield all-optical photonic switches. The photonic switches using `normally on' modulator pixels exhibit an output on-off ratio of 12:1 with internal optical gain of 4 dB. The photonic switches using `normally off' modulator pixels yield similar contrast and gain, but exhibit intrinsic bistable behavior. The inverted cavity modulators employed permit utilizing the transparency of the GaAs substrate at the operating wavelength and offer advantages for fabricating large arrays for optical signal processing     

AlGaAs/GaAs HBT的低频噪声

测试了AlGaAs／GaAsHBT的低频噪声，并将测试结果分解为1／f噪声、G－R噪声和白噪声，阐述了它们的产生机理，在此基础上建立了AlGaAs／GaAsHBT输入噪声电压的等效电路模型，该模型有助于AlGaAs／GaAsHBT电路的CAD。     

Traveling wave optical modulator using a directional coupler LiNbO3waveguide

Fabrication methods for low drive voltage and broad-band LiNbO3waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3c-cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps.     

Etching behavior of GaAs/AlGaAs multilayer structure during laser beam scanning

The thermochemical etching behavior of GaAs/AlGaAs multilayer structure during laser beam scanning has been studied. The etch rate changes between GaAs and AlGaAs epilayers as the etching process proceeds through the layered sample. The phenomenon can be explained by the difference of thermal parameters of the heterojunction interface. The local temperature rise from laser irradiation has been calculated to investigate etching characteristics for GaAs and AlGaAs. It is concluded that the good thermal confinement at GaAs/AlGaAs interface produces the wider etch width of GaAs layer than that of AlGaAs layer in GaAs/AlGaAs multilayer. The maximum etch rate of the GaAs/AlGaAs multilayer was 32.5 μm/sec and the maximum etched width ratio of GaAs to AlGaAs was 1.7.     

应用于40Gb／s电吸收调制器的Al2O3高速热沉研究

设计制作了面向40Gb/s电吸收调制器(EAM)的高速微波过渡热沉,并进行了EAM管芯级封装测试的验证.这种基于氧化铝(A l2O3)的热沉采用共面波导(CPW)传输线以实现低损耗微波传送,以及Ta2N薄膜电阻用于EAM的阻抗匹配.采用Ti/Cu/N i/Au金属材料作为CPW传输线电极材料,从而保证CPW传输线与Ta2N电阻材料之间良好的电接触,使热沉的典型反射系数在0~40 GHz范围内均达到优于-21 dB的水平.作为验证,采用该种热沉用于高速EAM的管芯级封装,测试得到小信号调制响应带宽超过40 GHz.     

Photoconductive response time of a multiple quantum well pinmodulator

Excite and probe measurements on a GaAs/AlGaAs multiple quantum well pin modulator using sub-picosecond optical pulses are reported. The quantum confined Stark effect allows measurement of a limiting rise time of 170 ps for establishing crosswell photoconductivity     

Collector-top GaAs/AlGaAs heterojunction bipolar transistors for high-speed digital ICs

GaAs/AlGaAs collector-top heterojunction bipolar transistors with magnesium and phosphorus double-implanted external bases were fabricated. A cutoff frequency of 17 GHz and a gate delay time of 63 ps for DCTL were obtained. These results indicate the potential of collector-top HBTs for high-speed ICs.     

Electric-field-dependent photoresponse of multiple quantum well modulator

By monitoring the quantum confined Stark effect using sub-picosecond laser pulses, the authors time resolve the field dependence of the photoconductive impulse response of a GaAs/AlGaAs multiple quantum well pin modulator.<>     

Technique for velocity-matched traveling-wave electroopticmodulator in AlGaAs/GaAs

A design for a velocity-matched traveling-wave directional-coupler intensity modulator in AlGaAs/GaAs is proposed. The structure utilizes a thin coating of Ta₂O₅ on the top of the modulator/electrode structure in order to achieve velocity matching between the optical wave and microwave signal. The film does not significantly affect the optical properties or voltage requirements of the modulator. The optical and RF characteristics of the modulator are analyzed using the effective-index and finite-difference methods. The optical bandwidth is calculated numerically, taking into account both the anticipated velocity mismatches due to fabrication tolerances and the calculated frequency-dependent microwave losses. The predicted small-signal bandwidth of a 3 mm long direction coupler biased at a null point is greater than 45 GHz, and exceeds 100 GHz (~50 GHz electrical bandwidth) when the coupler is biased in the linear region. This device is designed to operate at 830 nm with a maximum modulation voltage of 5 V. The figure of merit of the proposed device is therefore at least 10 GHz/V when an electrical bandwidth of 50 GHz is used     

Planar, linear GaAs detector-amplifier array with an insulatingAlGaAs spacing layer between the detector and transistor layers

Monolithic, high-speed planar, linear, parallel channel, ten-element GaAs detector-amplifier arrays with a 70- μm detector center-to-center spacing have been fabricated using a GaAs-AlGaAs-GaAs epitaxial structure grown on semi-insulating GaAs. The AlGaAs layer provided excellent electrical isolation between the transistor and n-type photoconductor epitaxial layers. Rise and fall times of integrated detector-amplifier array channels of 650 ps and 1.1 ns, respectively, were measured at 0.84- μm wavelength. The sensitivity of single, discrete, detector-amplifier channels was better than -34 dBm     

Breakdown behavior of GaAs/AlGaAs HBTs

Avalanche breakdown behavior at the collector junction of the GaAs/AlGaAs HBT (heterojunction bipolar transistor) has been studied. Junction breakdown characteristics displaying hard breakdown, soft breakdown, and negative resistance breakdown behavior were observed and are interpreted by analysis of localized microplasma effects, uniform microplasma-free behavior, and associated current gain measurements. Light emission from the collector-base junction of the GaAs/AlGaAs HBT was observed and used to investigate breakdown uniformity. Using a simple punchthrough breakdown model, the theoretical breakdown curves at different collector doping concentrations and thicknesses were computed and found to be in agreement with maximum breakdown voltages measured from devices displaying the most uniform junction breakdown. The serious current gain degradation of GaAs/AlGaAs HBTs at low current densities was analyzed in connection with the measurement of a large collector-emitter breakdown voltage. The unexpected functional relationship between the collector-emitter breakdown voltage and collector-base breakdown voltage is explained by the absence of a hole-feedback effect for devices not exhibiting transistor action     

Transient simulation of heterojunction photodiodes-part II:analysis of resonant cavity enhanced photodetectors

The high-speed response properties of resonant cavity enhanced (RCE) photodetectors have been investigated. The limitations on the high-speed performance of photodiodes and the advantages of RCE-detection are discussed. Transient response of heterojunction photodiodes under pulsed optical illumination has been simulated using the method described in Part I. Results on conventional AlGaAs/GaAs and RCE GaAs/InGaAs heterojunction p-i-n photodiodes are presented. For small area detectors, almost 50% bandwidth improvement along with a two-fold increase in efficiency is predicted for RCE devices over optimized conventional photodiodes. A nearly three-fold enhancement in the bandwidth-efficiency product was shown     

Novel GaAs/AlGaAs guided-wave analogue/digital convertor

The authors describe a high-speed guided-wave electro-optic analogue/digital convertor, designed and implemented in GaAs/AlGaAs using a novel configuration. Error-free operation of a 4-bit device has been demonstrated.<>     

A 20-GHz frequency divider implemented with heterojunction bipolar transistors

This paper reports a high-speed frequency divider implemented with AlGaAs/InGaAs/GaAs heterojunction bipolar transistors (HBT's). The divide-by-four static frequency divider was fabricated with a fully self-aligned dual-lift-off HBT process. A maximum operating frequency of 20.1 GHz was achieved. This is the highest frequency ever reported for static frequency dividers.     

Ohmic contact penetration and encroachment in GaAs/AlGaAs and GaAsFETs

Hypoeutectic AuGe/Ni ohmic contacts on GaAs and GaAs/AlGaAs were characterized by SEM, TEM, and energy dispersive X-ray analysis. The two main components of the contact were confirmed to be NiGeAs islands distributed in an Au-Ga alloy. The NiGeAs islands were larger and more evenly distributed on GaAs MESFETs than on GaAs/AlGaAs MODFETs. Vertical penetration was impeded but not halted by AlGaAs. Since the contacts did not melt during the alloying cycle, there was no lateral encroachment observed     

Effect of GaAs/AlGaAs quantum-well structure on refractive index

We investigate the refractive index difference between the GaAs/AlGaAs quantum wells (QWs) and bulk AlGaAs. We find the refractive index difference is smaller when the electric field in the nominally intrinsic MQW region is larger, or when the well (GaAs) thickness of the QW's is larger, or when the Al fraction of the QWs is smaller. The maximum refractive index difference between the 100 Å GaAs/100 Å Al_0.2Ga_0.8As QWs at zero electric filed and bulk Al_0.1Ga_0.9As is about 0.044. Even with a small refractive index difference of 0.0132, the OFF-state reflectance of a normally-off MQW modulator at the designed photon wavelength will increase from the desired value of 0% to 90% when the reflectivity of the bottom mirror is 0.99     

Electroabsorption waveguide modulators at 1.3 /spl mu/m fabricated on GaAs substrates

An InGaAs-InAlAs multiple-quantum-well (MQW) electroabsorption (EA) waveguide modulator fabricated on a GaAs substrate has been designed and characterized at 1.3-/spl mu/m wavelength for microwave signal transmission on an analog fibre-optic link. The modulator structure with a lattice constant 2.5% larger than that of GaAs is grown upon a 0.7-/spl mu/m-thick three-stage compositionally step-graded In/sub z/Al/sub 1-z/As relaxed buffer. The waveguide modulator exhibits a high-electrooptic slope efficiency of 0.56 V/sup -1/, a 3-dB electrical bandwidth of 20 GHz, and a large optical saturation intensity in excess of 17 mW. These high-speed optoelectronic modulators could potentially be integrated with on-chip GaAs electronic driver circuits.