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The base of heterobipolar transistor can be doped to much higher levels than can the base of the homojunction transistor. We describe the principle, operation and effusion properties of a home-made boron source for p-type doping of the SiGe base of the heterobipolar transistor. Transistors fabricated from the material grown by molecular beam epitaxy, with a boron-doped base, exhibit good d.c. characteristics. A current gain of β max = 1000 could be obtained with 10 18 cm −3 base doping.

Si/SiGe heterostructure bipolar transistors (HBT) were fabricated and compared to Si homojunction transistors with the same doping levels. Low-temperature Si-MBE was used to form the heterojunction and the homojunction layer sequences. One HBT structure has a graded-gap base layer, where the Ge fraction is 20% at the emitter side and linearly graded to 0% toward the collector side. This gives an average Ge content of 10% in the base and increases the critical thickness. The second HBT structure has a spike-doped S-base, sandwiched to low-doped SiGe layers. A strain selective etching technique was used to contact the thin base layer. Both HBT structures exhibit a higher current gain than the homojunction structure. >

Two Ka-band amplifiers in coplanar waveguide (CPW) technology are presented. The four-stage design is based on 0.3- mu m MESFETs, whereas in the three-stage amplifier 0.25- mu m high-electron-mobility transistors (HEMTs) are used. The monolithic microwave integrated circuits (MMICs) are designed for a gain of 20 dB. The authors present the realized MMICs and in particular the way in which typical difficulties arising from transforming theoretical demands into a coplanar circuit layout can be overcome. The applicability and accuracy of the developed design procedures are demonstrated by comparison of simulated and measured results. >

We have measured the hot-electron luminescence of GaAs HEMT devices over a broad spectral range in the infrared (0.4-1.4 eV). The emission intensity has spectral features suggesting that k-conserving, interconduction-band transitions dominate the emission process. The interpretation of emission spectra in terms of a hot-carrier distribution requires consideration of band-structure effects. In general this tends to reduce values of electron temperature Tel determined by the exponential fit to the experiment.

A systematic investigation on the breakdown mechanisms in the on-state mode of operation of pseudomorphic InAlAs/In/sub x/Ga/sub 1-x/As (0.53 >

An investigation of the introduction of doping into the channel of Al/sub 0.25/Ga/sub 0.75/As/In/sub 0.2/Ga/sub 0.8/As HFETs to obtain high saturation currents and reasonable low noise performance is discussed. The device performance is experimentally compared to that of undoped channel HFETs having the same layer structure. For a 0.35- mu m gate length backside doped channel HFET a maximum transconductance of 625 mS/mm, a maximum saturation current at V/sub Gs/=+0.8 V of 720 mA/mm, a power gain cutoff frequency of 195 GHz, and at 18 GHz a noise figure of 1.1 dB with 17 dB associated gain were measured. >

A monolithic two-stage low noise amplifier (LNA) on InP substrate is presented. Coplanar waveguides and lumped elements are used for the matching and biasing networks. The circuit is fully passivated and contains common ports for the gate and the drain bias. The total chip size is 2 mm/spl times/1 mm. A gain of 15 dB and an input and output matching better than -8 dB were achieved at 60 GHz.

A Ku-band GaAs Linearizer Preamplifier Front End (LFE) has been developed for satellite TWT-amplifiers. The LFE is build in hybrid and pseudomorphic HFET MMIC technology. A variable gain MMIC amplifier, two medium power amplifier MMICs, and a power amplifier MMIC are integrated in the Front End. The LFE has been integrated with the short traveling wave tube (STWT). An improvement of 10 dB in the 3rd order intermodulation distance was measured for the LFE/TWT-system.

A new type of GaInP/GaInAs/GaAs layer structure for MODFET devices has been developed. The novel feature of this structure is a compositionally modulated, pseudomorphic GaInP barrier which is suited to achieve record breaking two dimensional electron densities in GaInP/GaInAs/GaAs structures. Densities upwards of 3/spl times/10/sup 12//cm/sup 2/ with single-sided doping, and over 5/spl times/10/sup 12//cm/sup 2/ with double-sided doping have been obtained. Furthermore, it is demonstrated that buffer layers as thin as 2.5 nm are sufficient to achieve electron mobilities of more than 6000 cm/sup 2//Vs (RT) for electron densities of 3/spl times/10/sup 12//cm/sup 2/ in MODFET structures grown on top of these thin buffer layers. MODFET devices fabricated on this type of heterostructure using only 10 nm thick buffers have output transconductances and pinch off characteristics competing favourably with AlGaAs/GaInAs/GaAs MODFET devices fabricated on MBE grown structures. Intrinsic transconductances of 700 mS/mm and ft and fmax values of 100 and 180 GHz, respectively, demonstrate the potential of the new Al free structures.

A number of civil applications such as motion sensors and communications systems are planned to use the Ka-band frequency range. An MMIC chip set for the realization of the millimeter-wave front-end has been developed. The key MMIC circuit functions for Ka-band communication systems have been fabricated. Low noise amplifiers, a medium power amplifier, mixers and a dielectric resonator oscillator (DRO) have been developed using a common 0.25 /spl mu/m PMHFET technology allowing the future integration of several key components on a single chip. A voltage controlled oscillator has been realized in a GaInP-GaAs HBT technology for improvement of the phase noise performance. Low noise Schottky diode upconverter and downconverter are also available in 0.25 /spl mu/m MESFET technology with buried n/sup +/ layer.

Subthreshold conduction in submicron MODFETs has been measured and can be well described by a model which includes the shifts of both the ideality factor and the threshold voltage with the drain voltage. A method for extracting the model parameters from measured data is described. Experimental results turn out that it is essential to introduce the shift of the ideality factor with the drain voltage to properly describe the subthreshold characteristics observed in submicron MODFETs. The model with all extracted parameters, incorporating gate junction leakage, is in good agreement with the experimental data for 0.25/0.3 μm AlGaAs/GaAs MODFETs.

The authors measure the spectrum of radiative emission from a high quality HEMT device and relate this to the energy distribution of the channel electrons. The discussion focuses on the intraband and interband contributions to the spectrum. The intraband, bremsstrahlung component gives evidence for very energetic electrons (Tel approximately=6000 K). The radiative recombination of carriers, however, is characterized by a very much lower temperature.

Quarter-micron InGaAs-GaAs dual-gate HEMTs connected as a cascode MMIC in a compact manner have been fabricated and investigated. The devices show a high output impedance and a very low feedback capacitance, resulting in a high-voltage gain factor /sub gm///sub gd/ of 125 and a C/sub gs//C/sub gd/ ratio of 45. The current gain cutoff frequency f/sub T/ is 45 GHz and the maximum stable gain is 23.5 dB at 10 GHz and 19 dB at 20 GHz. The pseudomorphic cascode HEMTs show a low-noise figure of 1.1 dB with an associated gain of 22 dB at 10 GHz, at 18 GHz the minimum noise figure is 1.9 dB with 16-dB gain. >

This paper demonstrates a comparison of two three-stage Ka-Band amplifiers in CPW-technique. The first MMIC is based on AlGaAs/GaAs HEMT devices with a gate length of 0.25?m. The second MMIC is realized with 0.25?m InAlAs/InGaAs HEMT devices on InP. Both of the applied types of transistors, the GaAs and the InP HEMT are characterized by a similar lateral layout. Therefore the idea has been investigated of making use of the identical circuit layout in both applications, the GaAs as well as the InP MMIC. Measurements demonstrate a gain of 18dB and 29dB for the GaAs and the InP amplifier, respectively. This increase of 11dB in gain confirms the benefit of the idea to just replace GaAs HEMT devices by InP based HEMTs in the same circuit layout. Especially in the case of MMICs in CPW technique the advantage of increased transconductance and reduced feedback capacitance of the InP HEMTs compared to their GaAs counterparts is achievable without any restriction concerning the circuit realization and chip handling.

A three stage monolithic low-noise HEMT amplifier has been designed and fabricated for Ku-band receiver applications. The key element for the ultra low noise figure of the amplifier is an AlGaAs/GaAs HEMT with 0.3 ?m gate length and a gate width of 120 ?m. Single devices have shown a noise figure of 0.7 dB and an associated gain of 11.5 dB at 12 GHz. A monolithic amplifier chip has demonstrated a gain of 21.5 dB and a very low noise figure of 1.4 dB at 13 GHz, the input and output return losses are better than ?30 dB and ?20 dB, respectively. These data represent the best results yet reported for a low-noise Ku-band MMIC amplifier on GaAs.

PM HFET based devices and circuits on GaAs substrates are developed for the low noise and for the power components of 20 GHz to 30 GHz communication links. Cut off frequencies in excess of 200 GHz, minimum noise figures below 1.4 dB at 30 GHz and below 0.9 dB at 18 GHz, output power densities of 0.6 W/mm with PAE of 44 % at 18 GHz, and 0.36 W/mm with PAE of 40 % at 30 GHz are achieved.

Quarter micron dual-gate MESFETs and pseudomorphic HEMTs connected as a cascode circuit have been fabricated and investigated. The devices exhibit a high output impedance and a very low feedback capacitance resulting in high voltage gain factors gm/gd up to 125 and a Cgs/Cgd ratio up to 45. The maximum stable gain obtained with dual-gate HEMTs is 23.5 dB 10 GHz and 19 dB at 20 GHz, the current gain cutoff frequency is 45 GHz. The cascode PHEMTs show a low noise figure of 1.1 dB with an associated gain of 22 dB at 10 GHz. These results represent the highest gain values and the best noise performance yet reported for dual-gate HEMT devices. With dual-gate MESFETs a dynamic range of more than 35 dB can be obtained for the insertion gain/loss up to 40 GHz by applying a DC voltage swing of 4 V at the second gate electrode. Thus these elements are very promising for gain controllable amplifiers for both low noise and high gain as well as for switching applications.

The design and fabrication of a monolithic 60 GHz low noise amplifier is presented. As active device very low noise pseudomorphic HEMTs with Fmax ? 200 GHz have been developed and fabricated using a full monolithic technology. A two stage amplifier has been fabricated having reflexion losses below 10 dB and a gain of 5 dB at 58 GHz.

It is shown that strained isoelectronically doped buffer layers grown on GaAs and InP substrates allow one to reduce the dislocation density as well as the deep level concentration. Photoluminescence measurements show an improved near gap luminescence and a reduced deep level emission. This has been also confirmed by DLTS measurements. The higher material quality is also reflected in the device performance. GaAs Schottky diodes (n ˜0.5 · 1016Cm-3) exhibit a leakage current of 100 pA up to 50 V reverse bias at room temperature even with large Schottky contact area of 125 μm × 60 μm. This technique allows the quality of electronic and optoelectronic devices to be improved.

This paper describes results of a study on the monolithic integration of AlGaAs light-emitting diodes with GaAs field-effect transistors on a conductive p-GaAs substrate. Using a selective growth technique, a horizontal configuration is fabricated that allows separate optimization of the two types of devices and provides a quasi-planar surface. This approach is compatible with the standard GaAs integrated-circuit technology. By inserting an undoped layer and a p-n junction between the active layer of the FET and the substrate leakage currents below 500 µA for bias voltage up to 9 V are obtained for these insulation structures. The emitted light intensity of the LED, connected in series with the FET, exhibits a nearly linear dependence on the driving gate potential. Temperature or optical crosstalk effects were not observed. Fall and rise times around 20 ns were measured from the pulse response characteristics. This switching time is limited by the LED whereas the FET and isolation layers were found not to affect the switching behavior of the circuit in this time frame.

Si/SiGe heterostructure bipolar transistors (HBTs) were fabricated and compared to Si homojunction transistors with similar doping levels. Low-temperature Si-MBE (molecular-beam epitaxy) was used to form the heterojunction and the homojunction layer sequences. A wet chemical selective etching technique was used to contact the thin (80 nm) base layer of the heterojunction transistor. A peak current gain of 200 to 400 was measured for the heterostructure devices, compared to a gain of two for the homojunction structure. The current gain collector current dependence of the heterostructure device could be due to surface recombination effects. >

GaAs/GaAlAs heterojunction bipolar transistors have been made and integrated to a seven-stage I2L-ring oscillator. The five layer sequence has been grown by MBE. The transistor operating upside down (inverted, collector on the top) exhibits a current gain up to 50 for one collector. A groove isolation technique has been used to isolate the gates from each other. The structure was planarized by polyimide, incorporated Ta thin-film resistors for the injectors as well as implanted resistors. A delay time of 3.0 ns at 60-µW power consumption has been achieved in the low power region which corresponds to a power delay product of 0,18 pJ and a minimum delay time of 700 ps has been obtained at 1 mW.

Lateral pnp bipolar transistors have been fabricated using Be implantation to define the emitter and collector areas. The base area (1 - 2 µm wide) has been protected against Be ions during implantation by SiO 2 and photoresist. The lateral straggling and diffusion during the anneling process reduces the base width, which can be adjusted with the annealing temperature and time. Between the active n-GaAs layer and substrate, a n-Ga 0.7 Al 0.3 As layer is deposited. The Be ions penetrating the GaAs/GaAlAs interface form a pn junction in the GaAlAs layer below the emitter and collector area. This reduces the current by several orders of magnitude through the parasitic emitter-substrate (base) diode compared to a GaAs pn junction, due to the higher band gap. For these devices with an effective base width of 0.5 µm, a current gain of 10 in common emitter configuration has been obtained.