Substrate removed GaAs-AlGaAs electrooptic modulators

A novel GaAs-AlGaAs electrooptic modulator utilizing push-pull metal electrodes was fabricated using substrate removal techniques and polymer integration. The scheme enables a significant drive voltage reduction over previous designs and should enable ultrahigh-speed adjustable chirp operation     

AlGaAs/GaAs HBT IC's for high-speed lightwave transmission systems

The implementation of multigigabit-per-second optical communication systems requires many high-speed electronic circuit components that meet stringent performance requirements. Several important research prototype circuits for fiber-optic transmission, implemented in a baseline AlGaAs/GaAs HBT process, are discussed. These include a 20 Gb/s decision circuit, a 27 Gb/s 1:2 demultiplexer, a 30 GB/s 2:1 multiplexer, a 27 Gb/s 4:1 multiplexer, and a 11 Gb/s laser driver IC     

Studies of high-speed metal-semiconductor-metal photodetector witha GaAs/AlGaAs/GaAs heterostructure

A GaAs/AlGaAs/GaAs heterostructure metal-semiconductor-metal photodetector (HMSM) with an active area of 100 μm×100 μm was developed and studied. The measured risetime of the device is 30 ps. The measured falltime is as short as 23 ps. The observed ultrafast response is attributed to the reduction of both the carrier transit time and the device capacitance due to the incorporation of the AlGaAs barrier layer. The HMSM is found to have a smaller saturation capacitance and saturates at a much lower bias voltage in comparison with the conventional MSM photodetector (CMSM). At a bias of 10 V, the full width at half maximum (FWHM) of the temporal response of the HMSM is more than 20% smaller than that of the CMSM. In addition, it is found that the peak impulse response for the HMSM is substantially larger than that of the CMSM under the same operation condition. Two-dimensional and equivalent circuit analyses were carried out to interpret the observed phenomena and to provide insight into the underlying physics     

MBE-grown AlGaAs/GaAs HBTs on InP substrate

AlGaAs/GaAs HBTs are fabricated on InP substrates for the first time. Preliminary results show a current gain of 5 at a collector current density of 2 × 104A/cm2 in spite of a dislocation density higher than 109/cm2.     

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.     

Novel doubly self-aligned AlGaAs/GaAs HBT

A novel, doubly self-aligned process technology for AlGaAs/GaAs heterojunction bipolar transistors (HBT) has been developed. This doubly self-aligned process enables self-alignment for all emitter, base, and collector contacts and the fabricated device occupies an area approaching the intrinsic device area. The resulting base-collector capacitance of a fabricated device is reduced below half of the base-collector capacitance of conventional devices. The reductions in the capacitance are reflected in the superior cutoff frequency and maximum oscillation frequency of the doubly self-aligned devices as compared with conventional devices.<>     

Wavelength dependence of high-performance AlGaAs/GaAs waveguide phase modulators

The wavelength dependence of doped, reverse-biased channel waveguide phase modulators with very high efficiencies are reported between 1.06 ?m and 1.53 ?m. Figures-of-merit ranging from 61°/V mm and 40°/V mm to 27°/V mm and 16°/V mm for the TE and TM modes, respectively, have been obtained. By deducting the easily calculated linear electro-optic and free-carrier plasma effects, the data gives the first real measure of the dispersion associated with the shift in the absorption edge. This dispersion, which is the primary contribution to the quadratic electro-optic effect in semiconductors, accounts for more than half of the measured phase shift at 1.06 ?m with the doping level used.     

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.<>     

Microwave properties of traveling-wave electrodes in LiNbO3 electrooptic modulators

The microwave characteristics of a traveling-wave electrode in electrooptic modulators on z-cut LiNbO₃ crystals with buffer layers with various dielectric constants are calculated by a quasi-TEM analysis. The theoretical results are compared with the measured results on z-cut crystals for coplanar waveguide (CPW) electrodes. The agreement between the calculated and the measured results is good     

GaAs/AlGaAs power heterobipolar transistor fabricated on silicon substrate

A GaAs/AlGaAs power HBT was fabricated on a silicon substrate, where the thermal conductance is reduced by a factor of 2.8 compared with that on bulk GaAs. Due to the newly developed monolithically grown ballast resistor in the emitter region, the experimentally fabricated device has shown the highest collector current of over 2.5 A for a device with an active device area of 0.14 mm/sup 2/.<>     

AlGaAs/GaAs heterojunction bipolar transistor circuits with improved high-speed performance

Using a self-aligned base contact process and proton implantation to reduce extrinsic base-collector capacitance, we have improved the high-speed performance of AlGaAs/ GaAs heterojunction bipolar transistor digital circuits. The cutoff frequency of the transistor fT with an emitter width of 2.0 ?m is 45 GHz. NTL ring oscillators have operated at 16.5 ps/gate and CML ring oscillators at 27.6 ps/gate. Frequency dividers (1/4) have operated up to 11 GHz with wafer-probe testing These are record speeds for bipolar circuits.     

AlGaAs/GaAs/AlGaAs DHBT's for high-temperature stable circuits

High-temperature devices are required for a large number of industrial applications. In order to demonstrate the feasibility of a high temperature operating circuit on GaAs an operational amplifier was designed and fabricated. A corresponding technology for transistors and circuits for operation up to 300°C with AlGaAs/GaAs/AlGaAs DHBT's is presented. For the amplifier circuit an open loop gain of 49.5 dB at room temperature and 35.8 dB at 200°C was measured, which is in good agreement with the circuit simulation. High temperature stability has been proven by a storage test at 400°C over 1000 h for the ohmic contact metallization and 200 h for the transistors     

GaAs/AlGaAs heterojunction emitter-down bipolar transistors fabricated on GaAs-on-Si substrate

GaAs/AlGaAs heterojunction bipolar transistors with emitter-down structure were fabricated on GaAs-on-Si substrate for the first time. A maximum current gain of 25 was measured at a collector current density of 6250 A/cm². This value is comparable with that from similar devices fabricated on GaAs substrates. This result, along with previous work on large-scale integration of emitter-down transistors, demonstrates the potential for high-level integration of bipolar devices on GaAs-on-Si substrates.     

GaAs/AlGaAs多量子阱空间光调制器入射角度特性研究

研究了GaAs/AlGaAs多量子阱(MQW)空间光调制器(SLM)在不同入射角度下的调制特性。对腔模位置与入射角度的关系进行了理论计算和实验验证,两者具有较好的一致性。当入射角在0°～75°之间变化时,腔模从871nm变化至845nm,可调节范围达26nm。当入射光从垂直入射变化为约45°入射时,SLM对比度从(CR)3.8提高到16.3,调制电压从9.5V下降至6.5V。理论分析和实验结果表明,入射角度调节能够有效提高GaAs/AlGaAs MQW SLM调制性能。     

Electroabsorption and electrooptic effect in SiGe-Si quantum wells:realization of low-voltage optical modulators

We have calculated the behavior of the band-to-band absorption coefficient in square, coupled, and graded bandgap Si_0.6Ge _0.4-Si quantum wells as a function of the transverse electric field. It is seen that due to the weak confinement of the electrons (ΔE_c⩽20 meV) the absorption of photons with energy equal to the interband transition energy can be reduced at very small values of the transverse electric field. This phenomenon lends itself to the design of efficient amplitude modulators. In addition, the resulting change in the refractive index is also large and the corresponding linear electrooptic coefficient is calculated to be as large as 1.9×10^-10 m/V in square wells. This effect could prove to be the basis for the realization of efficient Si-based electrooptic modulators. Device designs are discussed     

A new self-aligned AlGaAs/GaAs HBT based on refractory emitter andbase electrodes

A self-alignment technique for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) using refractory metal film, W, as the emitter and base electrodes is presented. A nonalloyed contact formation combined with selective reactive ion etching of W or WSi_x against GaAs and SiO₂ produces a self-aligned structure. An emitter contact that is thermally stable is obtained by using a Zn diffusion process to make the extrinsic base contact layer. An f_T value as high as 82 GHz was obtained. The self-alignment technique combined with the Zn diffusion process will achieve a much higher f_T if a thinner base HBT structure is used     

Multisectional modeling of high-speed electrooptic modulators integrated in a microwave circuit CAD environment

We present a new multisectional model for high-speed electrooptic modulators, fully integrated within the framework of a microwave circuit computer-aided design (CAD) suite (MWOFFICE). Starting from geometrical and layout parameters, the model allows both simple (traveling-wave) and complex (phase reversal, periodically loaded) structures to be assembled, analyzed, and optimized from the standpoint of the electrical and electrooptic response (including chirp effects) both in small-signal (analog) and in large-signal (digital) operation, exploiting standard simulator tools. At no additional effort, parasitic and passive elements (such as optical or electrical delay paths) can be directly included in the modulator schematic, and the effect of transitions and package parasitics can be readily accounted for at a circuit level. Moreover, model integration within a circuit CAD suite enables one to seamlessly perform driver and modulator design and optimization within the same monolithic or hybrid circuit environment. Comparisons with experimental and literature data and design examples are presented to validate the approach and stress its potential in the design of high-speed electrooptic modulators.     

Novel Type of Wide\|Bandwidth GaAs/AlGaAs Infrared Photodetectors

A novel asymmetrical GaAs/AlGaAs photoconductance infrared detector based on the new idea proposed in this paper has been developed,which uses the intersubband transition within the same conduction (valence) band due to infrared radiation.The detectors with two wells or six wells grown by Metalorganic Chemical Vapor Deposition (MOCVD) system are fabricated by etching a mesa size of 200μm×200μm.Evident infrared absorption on the wavelength from 5 to 10μm has been observed for two samples,so has the peak of negative differential conductance.It is demonstrated that the photocurrent together with the signal\|to\|noise ratio increases with the number of the wells,but have nothing to do with the increase of the noise current under the same electric field,i.e.,the voltage drops per period,as is different from the conventional GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIPs).The noise current is one order's magnitude lower than that of the conventional GaAs/AlGaAs QWIPs.It is anticipated that the photocurrent and detector performances can be improved further by increasing the number of wells and optimizing the structural parameters.     

Novel GaAs/AlGaAs multiquantum-well Schottky-junction device andits photovoltaic LWIR detection

The authors have demonstrated photovoltaic detection for a multiple-quantum-well (MQW) long-wavelength infrared (LWIR) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5×10^-14 A for a 100×100 μm² detector (designed for 10-μm response) at 40 K, nearly nine orders of magnitude lower than that of a similar MQW LWIR detector without the blocking layer. The ideality factor is ~1.01-1.05 at T=40-80 K. The measured Schottky-barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also report a measured effective Richardson constant (A**) for a GaAs/AlGaAs heterojunction using this blocking layer structure. The A** is ~2.3 A/cm²/K ²