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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 quality of III–V electronic and optoelectronic devices suffers from the unsatisfying properties of the single-crystal ingots available. This influences the device quality and uniformity of the electric data and limits the integration density as well as the reliability of semiconductor devices in general. A review is presented of the application of a single strained layer or a sequence of different layers, e.g. a strained superlattice, on top of a conventional substrate wafer, which enhances the material quality impressively and modifies the band structure of the original material. It is shown that the method can be applied to all epitaxial processes and materials. Special attention is given to the incorporation of isoelectronic impurities. The underlying physics is discussed and the importance of the van der Merwe condition for avoiding the generation of dislocation networks is shown. The ranges of isoelectronic doping and lattice mismatch required for enhancement of the material quality are discussed. Results are given for single epitaxial strained layers on GaAs(In), InP(As) and InP(Ga) grown by liquid phase epitaxy, metal-organic vapour phase epitaxy, molecular beam epitaxy, and low-pressure vapour phase epitaxy. The change in band structure in the epitaxial layer as a result of biaxial strain and its effect on the carrier mobility are demonstrated.

As a new high resolution electron beam resist, homogeneous and fine-crystalline lithium fluoride films were fabricated. For this purpose, a special evaporation process was developed. The advantage of lithium fluoride is the relatively low critical exposure dose, compared with other metal halides. The exposure characteristics of this resist have been studied and the high resolution capability in the range below 10nm is demonstrated. The critical exposure dose for a single line is between 200 and 800nC/cm, depending on film thickness and substrate. The properties of these films in standard RIE-processes were investigated and pattern transfer into SiO 2 was performed.

The influence of oxygen contamination on Si low pressure vapour phase epitaxy (LPVPE) at 800°C in the SiCl2H2−H2 system has been investigated. O2 was added intentionally with partial pressures between 10−8 and 2×10−4 mbar. The quality of the epitaxially grown silicon layers was determined by comparing surface morphology, defect density, Schottky diode characteristics and SIMS measurements. These four parameters are correlated and they reveal a drastic decrease in epitaxial layer quality for O2 pressures above 15×10−6 mbar. The critical oxygen pressure which has been until now considered as a limit for epitaxial growth can therefore be exceeded by one order of magnitude.

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. >

The formation of III–V-and related compounds and their optical and electrical behaviour are dependent on their position in the Periodic System of the elements.

Using GaAs-MESFETs under switching conditions, the regeneration and amplification of fast pulses in the 50ps range is performed. Sharpening factors t/sub y in/ / t /sub y out/ of 3 and voltage amplification factors of 2 at 50 ohm are reached for output pulses up to 100 mA.

GaInAs MISFETs with pyrolytic SiO/sub 2/ isolator on n- and p-GaInAs have been investigated with regard to analog and digital performance. The 1.7- mu m gate length MISFETs on n-GaInAs and p-GaInAs have transconductances of 100 mS/mm and 40 mS/mm, cutoff frequencies (f/sub T/) of 14 GHz and 2 GHz, and maximum frequencies of oscillation (f/sub max/) of 18 GHz and 6 GHz, respectively. Due to the self-aligned process and the better carrier confinement, the MISFETs on p-GaInAs show higher f/sub max//f/sub T/ values. An inverter on p-GaInAs with a high static voltage gain of -13.5 and high noise margin has been integrated to a 31-stage ring oscillator, proving the reproducibility of the technology with a pyrolytic SiO/sub 2/ isolator. The delay time of one stage is 6 ns, corresponding to an intrinsic frequency of 200 MHz, which shows that the operation point of the ring oscillator is not optimized. >

The capability of lithium fluoride based films as a self‐developing resist for ultra‐high resolution electron beam lithography is demonstrated. The advantage of lithium fluoride is the relatively low critical exposure dose, compared to other metal halides. Homogeneous and fine‐crystalline films have been deposited using a special evaporation technique. We studied the exposure characteristics of this resist and achieved patterns with lateral dimensions below 10 nm. The properties of these films in RIE‐processes were investigated and pattern transfer into SiO2 was performed.

Silicon etched-groove permeable base transistors (PBTs) which utilize a new structure to eliminate surface depletion effects are discussed. The 90-nm-wide fingers are n/sup +/-doped, and the channel region is buried below the bottom of the grooves. Doping and thickness of the active layer were optimized using two-dimensional computer simulations. The maximum measured transconductance of 155 mS/mm is the highest reported for Si PBTs and demonstrates the potential of silicon as substrate material. The measured transit frequency was 12 GHz; f/sub max/ reached 13 GHz. It has been recognized that for improved high-frequency performance a reduction of the gate capacitance is necessary, demanding a more precise control of groove depth and geometry. >

Silicon permeable base transistors (PBTs) with monocrystalline buried CoSi2 gates have been fabricated by local high dose cobalt ion implantation through a grid-like mask into epitaxial Si (100) layers and homoepitaxial Si over-growth by low-pressure vapour phase epitaxy. The PBTs show good DC characteristics and pinchoff at zero or at low negative gate voltages, respectively. Transistors with a grating periodicity of 0.6 μm reach a maximum trans-conductance gm of 70 mS/mm. The highest obtained transit frequency is fT = 6 GHz.

Homogeneous and quasiamorphous lithium fluoride based films have been deposited as a new ultrahigh resolution electron beam resist. The exposure characteristics of this self‐developing positive tone resist are discussed. Compared to other metal halide films, a high sensitivity is the most important advantage, while the resolution limit is also far below 10 nm. Concerning pattern transfer, the properties of this resist in various reactive ion etch processes and the capability for a lift‐off process were investigated.

This paper is devoted to pure Au quantum wires with a length varied between 50 nm and 1 μm. In order to obtain extremely pure metallic nanometer structures, a liftoff process is preferred. To overcome the problem of grain size limited linewidth control and edge quality, a four‐layer resist system for electron beam lithography has been developed, which enables the reproducible fabrication of mesoscopic devices with lateral dimensions down to 25 nm. I–V characteristics and magnetoconductance measurements have been carried out. Especially in the case of short wires, where electron transport is in the quasiballistic regime, universal conductance fluctuations have been observed, which are visible even at temperatures above 30 K.

By lowering the reaction temperature in an LPCVD system to 1053 K to a pressure of 21 Pa, inverted camel diodes with excellent DC properties have been grown. The n/sup ++/p/sup +/n/sup -/n/sup +/ structures grown onto n/sup +/-Si substrates

GaInAs camel transistors with a current gain of 6.7 at room temperature have been fabricated for the first time. The layers were grown by MOVPE. High frequency measurements on devices with an emitter area of 64 μm 2 give a transit frequency of 1.7 GHz. Hot electron spectroscopy at 100 K shows two peaks of the energy distribution belonging to hot electrons with and without intervalley scattering

A double Schottky interdigitated photodetector has been fabricated on GaInAs. The active layer of 0.7 μm thickness was grown on semi-insulating InP substrate by LPE. For x-ray lens application, Fresnel zone plates with 100 zones and a width of the outermost ring of 50 nm have been etched into AuPd. They are carried by a thin Si 3 N 4 membrane providing good radiation transmission for optimum efficiency. To demonstrate the system performance, test structures for multi-level fabrication and field stitching have been generated. Thereby the overlay accuracy of two mask levels proves to be less than 20 nm along a field of 90 μ × 90 μm. Stiching of subfields (size 100 μm × 100 μm) showes an error of just 40 nm at the edges of the deflection field.

Be and Cd ions were implanted into n-Ga0.47In0.53As. SIMS profiles show in both cases a high diffusion towards the surface during the annealing procedure. In addition, Be exhibits a significant diffusion into the bulk crystal which depends on the capping layer. A Si3N4 cap leads to a higher residual Be concentration in the implanted region. Damage caused by As implantation reduces the indiffusion remarkably. An electrical activation of about 50% of the implanted Be atoms could be achieved, whereas even annealing temperatures of 800°C activated only a small part of the Cd atoms. I–V characteristics of Be p-n diodes showed abrupt junctions with ideality factors of about 1.6. Cd diodes exhibited a soft breakdown and ideality factors of 2.

In the presentation the problems are stressed which occur in nanometer lithography. A 100 keV-e-beam system is demonstrated which consists of a modified STEM linked to a PDP 11 computer for (3 nm) 2 pixel size definition. The feedback loop for exposure dose stabilization is shown as well as the alignment procedure. The limitations of the system are discussed. The resolution is shown to be dependent on the spherical aberration at given focal length and scan field. The application of the presented system is demonstrated showing characters with (20 nm) 2 pixel size, gold zone plates with minimum linewidths of 50 nm, aspect ratios of up to 5:1, and a rectangular shaped measuring structure for magneto-quantum effects.

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.

Using GaAs MESFET's under switching conditions, the regeneration and amplification of fast pulses and the modulation of semiconductor lasers in the Gbit/s speed range is performed. Sharpening factors of 3 at output pulse rise times of nearly 50 ps and voltage amplification factors of 2 at 50 /spl Omega/ are attained for output pulses up to 100 mA. The regeneration is caused by the clamping at the input port of the MESFET and by the nonlinear transconductance characteristic. In the pulse modulation mode, the laser diode is directly controlled by the MESFET. The switching behavior of the driver stage is calculated using the equivalent circuit of the laser diode and of the MESFET. This evaluation reveals that the maximum pulse rate is limited by the laser diode.

GaAs p-n mesa diodes have been made with the aid of a laser stimulated MOCVD process. Using ns laser pulses the deposition of epitaxial GaAs is limited to the irradiation area. For irradiation a Nd-YAG pulse laser (frequency double, λ = 530nm) has been used. Firstly, an n-type layer was deposited with the conventional MOCVD process at 650°C. Then in the same system, at a substrate temperature of 450°C, a 2.5μm thick p-type mesa was grown using 120mJ/cm 2 pulse energy and a pulse repetition rate of 5Hz. The diodes produced this way, showed ideality factors of 1.75 and breakdown voltages of higher than 12V.

Recent progress in the development of GaAs thin film photoconductive detectors for future optical communication systems at near-IR wavelengths is reported. The devices consist of a thin high purity epitaxial layer of GaAs grown on top of a chromium-doped semi-insulating substrate, two metal contacts and a contact layer on top of the “active” layer. Intrinsic detector response times of the order of 28 ps are found after excitation with fast laser pulses. The initial fast photocurrent decay is followed, if and only if the contacts are ohmic, by a second decay which is orders of magnitude slower. The amplitude of the slow tail decreases and finally disappears at higher excitation intensities or after the superposition of extremely faint continuous wave light. It is suggested that a small number of deep centres which are present in the active layer or close to the interface with the substrate (probably chromium) and which trap and re-emit charge carriers are responsible for the long tail. These centres are saturable. The results of studies of current gain and noise equivalent power of GaAs and a comparison with In0.53Ga0.47As/InP detectors are given and possible means of future improvements are indicated.

Intrinsic large signal rise and fall times of less than 30 ps without charge storage demonstrate the potential of single and dual gate GaAs MESFETs for Gbit/s optical communication systems. The applications as signal regenerator, bit synchronizer, laser modulator, multiplexer, and demultiplexer are shown. Using only one dual gate GaAs MESFET clock and pulse shape regeneration as well as 1 Gbit/s laser modulation is performed. Bit synchronization is demonstrated up to 4 Gbit/s. 1 to 2 Gbit/s and 2 to 4 Gbit/s multiplexing as well as 2 to 1 Gbit/s demultiplexing with additional clock and pulse shape regeneration is shown using dual gate FETs. 2 to 4 Gbit/s multiplexing without clock regeneration is also accomplished using single gate GaAs MESFETs.

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.

Low energy ion implantation (2–10 keV) of beryllium has been performed and annealing carried out by rapid thermal annealing at different temperatures. Secondary ion mass spectrometry measurements of implanted profiles showed a strong diffusion of the beryllium atoms towards the surface. For the lowest implantation energies this influence is so strong that no indiffusion could be measured. The resulting annealed profile is much narrower than the implanted profile. From diodes fabricated from these layers, a barrier enhancement of 0.42 eV has been determined.

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.

GaAs has an advantage over Si and Ge in some material parameters for bipolar transistor application. Another benefit is the availability of the wide gap emitter principle for GaAIAs/GaAs heterojunction transistors. Such bipolar transistors have been fabricated and tested. Maximum frequency of oscillation f MAG = 2.2 GHz and cut-off frequency f T = 2.7 GHz demonstrate the high-frequency suitability, whereas emitter-collector breakdown voltages V CEO 100 V and maximum collector currents I C max ∼ 300 mA are an indicator of high-power applications. The transistor operates at temperatures in the range of − 269°C to + 350°C. A double heterostructure NpN transistor shows the elimination of the turn-on voltage of ∼ 0.2 V for Npn wide gap emitter Ga 0.7 Al 0.3 As/GaAs transistors in common emitter configuration. The NpN transistor can be operated in bi-direction with comparable current gain due to the wide gap emitter principle and the symmetry of the emitter-base and collector-base heterojunctions. Compared with the Npn GaAs transistor, the storage time t s of the NpN GaAs transistor is reduced by a factor of about 2.

It has been shown that with Ga or As doped InP epitaxial layers exhibit improved material quality [H. Beneking et al., Appl. Phys. Letters 47 (1985) 828]. By proper choice of the doping content a reduction of dislocations as well as a minority carrier diffusion length enhancement are achievable [H. Beneking and N. Emeis, IEEE Electron Device Letters EDL-7 (1986) 98]. It is demonstrated that the application of this technique allows one to fabricate bipolar diodes with improved electrical characteristics. The application of the strained layer growth in conventional device processing steps as dopant indiffusion and multilayer epitaxial growth is demonstrated. Furthermore, the uniformity of the parameters is greatly enhanced, which will be shown by presenting data on the standard deviation of reverse currents on 1 cm 2 wafers.

Thin layers of GaAs are heavily doped locally by laser induced Se or Zn diffusion. H2Se or diethylzinc gases are used to provide Se or Zn dopant atoms. The surface is locally heated with 3 ns light pulses from a Q-switched frequency doubled Nd-YAG laser. The doping process is described in detail. Doping profiles and sheet carrier concentrations are measured as a function of substrate temperature, laser fluence and processing time. Dopant concentrations of more than 1021 cm−3, with a thickness of the doped layer of less than 20 nm can be achieved.

Epitaxial layers of Ge have been grown on GaAs〈100〉 substrates by thermal decomposition of GeH 4 in hydrogen at atmospheric pressure. Growth was investigated for growth temperatures between 400 and 700°C at growth rates of 0.1−10 μm/h. Two different growth areas were observed. Above 500°C the growth is nearly constant and mainly limited by gas phase diffusion. Below this temperature, the growth rate decreases rapidly. For low temperature growth, an activation energy of 1.4 eV was found. Layers deposited at high temperature show good crystallinity but highly doped thin interfacial layers due to Ga and As diffusion. This effect is reduced at low temperatures. At 400°C smooth layers have been deposited with a background doping below n = 10 17 cm -3 .

By low pressure vapour phase epitaxy, epitaxial growth down to 819°C has been achieved in the SiCl 2 H 2 /H 2 system. High and homogeneous in situ p-type doping has been realized with boron in the range 2 × 10 18 −5 × 10 19 cm -3 , with relative steep transition to be substrate. Under near-equilibrium growth conditions, selective growth results with reproducible growth rates of 8–60 nm/m. The crystalline quality of the low temperature epilayers has been investigated on a p-n junction with encouraging results.

We present a novel MOVPE reactor using a rotating substrate holder. It is the second generation of a susceptor that uses a frictionless gas bearing to carry the rotating part being driven by hydrogen. The susceptor is capable to rotate a two-inch diameter wafer at a rate of up to 1 revolution per second. The Ga0.47In0.53As layers grown at atmospheric pressure and a gas velocity over the substrate of 15 cm/s show a standard deviation of layer thickness of σ=±0.96% and composition variations of less than 1% within an area of 4 cm diameter.

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.

It is shown that thickness uniformity of OMVPE layers can strongly be improved by rotation of the substrate during growth. A new susceptor assembly to achieve rotation is presented.

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.

In this paper we present a camel diode in GaInAs on a InP-substrate with an ideality factor of 1.6 - 1.7. The barrier height is 0.44 eV. Switching measurements show no storage time and a fall time of 660 - 740 ps for a 50 ?m * 50 ?m device.

The electrical characteristics of Schottky diodes fabricated on silicon surfaces subject to low energy (10 keV) Ar + implantation have been studied as a function of Ar + ion dose. Significant changes in electrical characteristics are seen for ion doses as low as 5×10 11 cm -2 , well below the amorphization threshold dose for silicon. In conjunction with the ion energy threshold established earlier for silicon surface damage effects (about 25 eV), these results outline fundamental limits on the effect of ion-assisted dry etching processes on silicon surface barriers.

A new system to grow single crystal epilayers by metal organic chemical vapor deposition is presented. The graphite susceptor is heated by a 750 W quartz-halogen lamp. To focus the light onto the backside of the susceptor an elliptical mirror is used. With this system epilayers of good quality on GaAs are grown down to 600°C. The morphology, background doping and mobility as a function of growth conditions is shown. Highly doped layers are grown with H2Se and DEZn (Diethylzinc).

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.

The degree of radiation damage in PMOS and NMOS transistors fabricated in astandard N-well process due to deep ultraviolet (DUV) ArF excimer laser (193 nm) irradiation was determined by measurement of the subthreshold characteristics. Depending on the pulse energy density and the dose different shifts in the drain and in the leakage current occur. All induced radiation damage was annealed after a 450°C temperature step in N2 and 10% H2 for 20 min. The intensities necessary to induce significant radiation damages are much greater than those required for DUV lithography.

A sheet of donor atoms is embedded in GaAs only 200 A below the surface. The Schottky contact is used as a barrier for the tunneling curent between the subbands of the doping layer and the surface metal. The energies of occupied and unoccupied levels are determined from distinct structures in the first derivative. The comparison with a self-consistent calculation yields the densities of free carriers, δ-doping, and background doping.

Ohmic contacts of Au and Ag based Zn containing alloys on p -type Ga 0.47 In 0.53 As have been studied using intermediate layers of Ti and Ni, respectively. Low specific contact resistance in the order of 10 −5 Ωcm 2 are achieved. In case of AuZn alloy, the Ti intermediate metal layer causes higher contact resistances together with a worse contact morphology in contrast to Ni intermediate layers. However for AgZn contacts Ti adherent layers improve the contact resistances, especially for lower alloying temperatures. Moreover these contacts exhibit significant smoother interfaces as revealed by TEM micrographs. Thus AgZn contacts apply best to low resistive contacting of very thin p -layers forming e.g. the base of a ballistic device.

GaAlAs and GaAs epitaxial layers were grown in a radiation heated reactor using metalorgonic compounds. Sequential combinations of GaAlAs and GaAs layers were used to form contacts to p-type layers. These heterostructures have the advantage of allowing the use of selective etching steps. Highly doped p-Ga1-xAlxAs layers for x = 0.5 were grown with smooth surfaces at temperatures above 625δC. The layers are homogeneous in thickness, resistivity, and aluminum molar fraction, SIMS measurements showed sharp Zn profiles. To prevent oxidation of the GaAlAs layer, a 0.2 μm thick GaAs protection layer was deposited as a last step. Metal layers like Al, Ti/Au, or Ti/Pt/Au were evaporated to form ohmic contacts without any alloying. Contact resistances as low as 8 × 10-5 ω cm2 have been obtained.

Two topics in the liquid-phase epitaxy of lattice-matched Ga 0.47 In 0.53 As layers on InP were studied. First, the addition of PH 3 to the H 2 ambient to prevent thermal decomposition of the substrates can be optimized to obviate the incorporation of P into the ternary layers. Secondly, Mg was used as an acceptor in both InP and GaInAs which was found to exhibit a smaller diffusion coefficient and activation energy, as well, as compared to Zn.

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