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The functional behavior of the collector part of an amplifying three terminal electronic device is reviewed, relevant for transport and collection of carriers. The important properties are analyzed, with emphasis on III-V materials. The resulting demands are deduced, and conventional as well as unconventional solutions in the case of unipolar devices (FETs) and bipolar devices (HBTs) are presented. They include bandgap and doping profiling, heterojunction- and Schottky-collectors. Not considered are thermal stability problems and further DC phenomena, relevant for high-power devices.

The fabrication of overgrown silicon permeable-base transistors (PBTs) is described starting from MBE-grown epitaxial Si/CoSi/sub 2//Si heterostructures. Gate fingers are patterned by Ar sputtering followed by low-pressure vapour phase epitaxial overgrowth at 800 degrees C and 0.2 mbar. Results on surface morphology, Schottky-diode characteristics, and PBT performance are presented. It has been recognized that a serious problem of Si PBTs is the field crowding effect at the rim of the thin silicide gate. It cases breakdown at low voltages and limits PBT performance. A diagram indicating the possible operating areas depending on silicide thickness, channel doping, and PBT geometry is presented. >

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.

Silicon MESFET ring oscillators have been successfully fabricated on low- and high-resistivity substrates. Contact printing was used as optical lithography to produce gate lengths of 1 µm. Despite the simple fabrication process the ring oscillators exhibited switching times of 0.7 ns at a speed-power product of 35 fJ. The degradation of device performance by backgating and the dependence on substrate doping was investigated.

The influence of the epitaxial structure (doping profile) in the channel region of a GaAs MESFET on its small signal scattering parameters is investigated both theoretically and experimentally. The large signal frequency behavior of FET's with a buried channel is compared with that of uniformally doped FET's. In the case of buried channel devices a much smaller variation of the s parameters with frequency is observed. This phenomenon can be understood by considering the inner transistor to consist of a two-dimensional transmission line. The principle of this new model, which is mainly based on technological data, is presented. Furthermore, the improvement of the nonlinear distortion is investigated. The FET's with a graded doping profile show very small intermodulation products, -42 dBm for an input power level of 4 dBm (P out = 9 dBm: 1-dB gain compression) at a relatively small drain-source voltage of only 4 V.

A new technology of ion-implanted silicon MESFET's on high-resistivity substrates has been developed to reduce substrate effects. Consequently, the devices show an improved static behavior concerning pinchoff and drain feedback. Static and dynamic performance will be presented, the latter showing f_{max}=14 GHz calculated from scattering parameter measurements and a large signal switching time of 60 ps. The transit frequency of the intrinsic device is f_{T} \sim 3.9 GHz.

On p-type Ga 0.47 In 0.53 As LPE-grown layers, Schottky diodes were fabricated with different metals and surface preparations. On chemically etched surfaces, diodes with ideality factors near unity but rather low breakdown voltages with soft breakdown were achieved. The barrier heights were between 0.4 and 0.7 eV depending on the work function of the metal. On sputter-cleaned surfaces the diodes exhibited high breakdown voltages and barrier heights of about 0.7 eV independent of the metal. Annealing of the diodes at 320°C resulted in reduced series resistances and barrier heights in the case of sputteretched surfaces. The junction seems to consist of two different barriers; the lower one is determined by an As segregation at the interface, whereas the higher one is caused by traps which are induced by the sputter process.

Fast optical detectors use photoconductive effects in semiconducting channels or thin films. The behavior of those planar and coaxial detectors is reviewed. It is shown that p-type and n-type materials show different behavior in respect to bandwidth and gain. The strong influence of the contacts is clarified and the surface recombination is taken into account. The bandwidth of those detectors is evaluated and the gain and gain bandwidth product are given in terms of the geometry and material data. Furthermore, the influence of deep levels and of a depletion layer along the surface is considered, which considerably affect the static characteristics as well as the pulse response. Regarding these effects, the different behavior of GaAs- and Ga 0.47 In 0.53 As-conductive photodetectors is demonstrated.

A monolithic wavelength converter has been constructed in the GaAlAs alloy system which comprises a wide gap emitter phototransistor and a double heterojunction (DH) light emitting diode (LED) in a bifacial configuration. The liquid phase epitaxy (LPE)-grown structure is capable of efficiently converting IR light with λ < 870 nm into the red spectral range in conjunction with optical power amplification.

Macroscopic analog models of planar contacts to semiconductor layers were made and equipotential lines underneath the contact were traced. Voltage drop and current density across the interfacial layer of such contacts were determined and compared to theoretically calculated values. The extended transmission line model (TLM) is used to describe the measurements and a reasonable limit for its application to the measurement of ρ c is \rho_{c}/(\rho_{s} . h) > 0.2 ; for \rho_{c}/(\rho_{s} . h) \le 0.2 the model of Overmeyer appears to be applicable.

Different materials and different types of detectors are used for optical data communication in the wavelength range of \lambda \sim 0.8 µm \lambda \sim 1.7 µm. In this paper the behavior of p-n diodes, Mn and Mp Schottky diodes is evaluated as well as that of bipolar transistors, n-p-n and p-n-p, and of photoconductive detectors using n-type or p-type material. The different behavior of lateral and coaxial versions is shown taking into account contact and surface recombination. The gain, the bandwidth, the gain bandwidth product, and the rise time of all these types of fast detectors are given in terms of material and technological data, including the discussion of the different rise and fall times of some detector versions. Finally, a theoretical comparison is made between the detectors showing their different behavior and ultimate performance limit. For practical GaAs planar devices as a photoconductive detector, a p-n diode, a heterojunction n-p-n and a lateral n-p-n transistor, a Mn Schottky diode, and a totally depleted MnM structure (symmetrical Mott barrier) experimental data are given. They verify the theoretical prediction that with all types of detectors rise times of

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.

The specific contact resistance ρ c of Ni/Au-Ge/Ni and Ni/Au-Sn/Ni layers on n-GaInAs and Ni/Au-Mg/Ni and Ni/Au-Zu/Ni on p-GaInAs are measured for different alloying temperatures and times using an extended transmission line model. Specific contact resistances of 4.10-8Ω cm2for Ni/Au-Sn/Ni on n-GaInAs (n = 1018cm-3) and 2.10-5Ω. cm2for Ni/Au-Zn/Ni on p-GaInAs (p = 1018cm-3) are obtained. After deposition at room temperature, the barrier height of the metal-n-GaInAs system was determined to be 0.16 eV, decreasing below 20 meV after heat treatment. Interdiffusion of metal and semiconductor was investigated by SIMS/Auger measurements. At alloying temperature of 300°C the contacts show fast diffusion of Au relative to the dopants, effecting an increase of the specific contact resistance.

The behavior of photocarriers in a GaAs planar n-channel device as an optical detector is studied. Computer simulations show that space charges of those photogenerated carriers give rise to a high-gain and high-speed amplification mechanism which results in Gunn oscillations at intense irradiations. Experiments have confirmed these oscillations. The observed results agree with theoretical computations.

Buried-channel GaAs MESFET's (BFET's) on MBE material have been fabricated. The bias dependence of the scattering parameters is strongly reduced applying the BFET principle. As a result the third-order intermodulation products are the smallest reported thus far,-45 dBm at an input power level of 8 dBm. These data are compared with those of VPE fabricated devices. The technology as well as the fabrication of the MBE layers is described.

A new concept for integrated planar Schottky-diodes has been developed. It meets the two important requirements in the design of microwave diodes: high cutoff frequency and low parasitics. Only one epitaxial layer is needed. The Schottky contact is deposited on the slope of a mesa in order to obtain both low series resistance and low capacitance, Up to now, a Zero-bias cutoff frequency of 150 GHz has been achieved. The advantage of this type of diodes as compared to planar diodes produced by double selective epitaxy is the use of standard technology, resulting in good reproducibility and yield.

Fast double-Schottky-interdigitated diodes have been fabricated by evaporating Al-Schottky contacts on lowly doped n-GaAs (n=1014cm-3), These detectors have a relatively large light-sensitive area of 400 µm2. Rise and fall times are in the order of 10 ps. The external quantum efficiency is 25 percent at λ = 820 nm. The frequency response of the diodes is essentially flat up to 18 GHz, which is the limit of the measuring equipment.

GaInAs metal-insulator-semiconductor field-effect transistors (MISFETs) have been fabricated on metalorganic vapor-phase-epitaxy (MOVPE) grown GaInAs layers. Enhancement-type MISFETs exhibit very high transconductances of 300 and 250 mS/mm for gate lengths of 1.5 and 3 mu m, respectively. The effective channel mobility is 5800 cm/sup 2/ V/sup -1/ s/sup -1/. The saturation velocity is 3.5*10/sup 7/ cm/s. High-frequency measurements performed on 3- and 1.5- mu m-gate-lengthdevices result in a current gain cutoff frequency of 6 and 14 GHz, respectively. >

It is shown that the drift velocity saturation of the current carriers in the channel of a MOSFET iS an important factor in the analysis of the electrical behavior of such devices. The theory presented here, which includes this effect, shows improved agreement with measured output characteristics.