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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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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 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.

A slightly modified MO-CVD process was used to grow epitaxial layers of GaP and GaAlP on GaP and Si substrates. PH3 is cracked before reaching the substrate by leading it through the hot susceptor. The morphology of epitaxial GaP layers is strongly dependent on substrate orientation and growth temperature. Layers with mirror-like surfaces are achieved on 3° off (100)GaP substrates at 730°C. The background doping level is n ≈ 3 × 1016 cm-3. Nitrogen doping was achieved by addition of NH3. This lowers the growth rate similar as in the halide process. CL spectra show the successful incorporation of N as isoelectronic impurity. First, non-optimized LED structures with external quantum efficiencies of 3 × 10-5 are realized.

For applications in an imaging X-ray microscope, Fresnel zone plates have been fabricated by electron beam nanolithography and suitable pattern transfer techniques. Images of biological specimens have been taken with a microzone plate of 250 zones and 55 nm outermost ring width at the electron storage ring BESSY in Berlin.

Solution-grown GaAs p-n junctions were formed simultaneously using three differently oriented wafers, namely, the

The generation of 15‐ps light pulses at 1.23 and 1.26 μm having 200 mW peak power at a repetition rate of up to 10 MHz from directly modulated unbiased V‐groove InxGa1−xAsyP1−y lasers is reported. Specially designed avalanche generators are employed for modulation of the laser injection current. The light pulses are analyzed using microstructured Ge photodetectors having a response of 62 ps at full width half‐maximum. A deconvolution technique based on a theoretical analysis of the complete circuit of the detection system is applied to reduce the large error occurring normally when the characteristics of fast pulses are determined from the response of much slower detectors. This technique is proved by independent experiments to hold. A spontaneous lifetime of 1.5 ns of the charge carriers in the active layer of the laser is determined from the measured delay times between the optical and electrical pulses.

We report the generation of short light pulses of 23‐ps duration from an unbiased proton implanted double heterostructure cw laser by direct gain modulation. Repetition frequencies up to 10 MHz and a typical peak power of 300 mW are achieved. The time behavior of the light output is largely independent of the rise and fall time of the modulation current, since the first relaxation oscillation of the laser is utilized.

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.

GaAlAs/GaAs bipolar phototransistors involving a wide gap emitter have been fabricated which exhibit high current gain with corresponding external quantum efficiencies of the order of 5000. The devices provide a power switching capability of more than 1 W.

GaAs/GaAlAs DH lasers isolated by an SiO 2 layer on top of the p-contacting layer are compared to DH lasers in which the isolation is maintained by an isolating the O+ -implanted layer within the n+- substrate. Measurements were performed on four O+ isolated lasers and five SiO 2 isolated lasers with the same composition and thickness of active and upper confinement layers. Threshold currents of both groups were very similar, whereas the O+ -implanted lasers showed superior thermal resistances by a factor of 2. Thermal resistances were measured by the shift of the lasing spectra with power dissipation.

Since its introduction in 1975 /1,2/, high-speed sampling of voltage transients on transmission lines using photoconductive switches has been of great interest. Besides superior equivalent bandwidth, it offers a dynamic range considerably larger than conventional sampling oscilloscopes, and complete isolation between the transmission line under test and the sampling circuit. Despite these advantages, it has never found widespread use outside the research area, mainly due to the costly ps dye lasers required. A sampling system using a semiconductor laser would resolve this problem, provided it has a temporal resolution equal or superior to conventional sampling oscilloscopes (≤25 ps). Besides the generation of ps pulses with semiconductor lasers /3/, which will not be discussed here, a photoconductive gate with a carrier lifetime ≤10 ps is necessary, yet sensitive enough to efficiently sample when controlled by pJ pulses from a laser diode.

With the aid of a 100 keV electron beam lithography system, microzone plates have been fabricated. The system has been designed for generating structures with lateral dimensions in the below 100 nm range. The particular demands on high resolution, high efficiency imaging Fresnel zone plates and the arising problems concerning lithography and pattern transfer are discussed. We will show a step by step improvement of fabricated microzone plates with an outermost zone width of 50 nm. A thin titanium intermediate layer is used as a stable mask to generate ion milled gold absorber rings with very steep walls. The zone plates have been tested by imaging one another in an X-ray microscope, and compared to the image obtained with the holographically fabricated MZP3 microzone plate from Gottingen (Schmahl et al., /1/).

Doping of semiconductors from a gas atmosphere is a technique which is well established in device technology. However, little has been reported about short-time laser-induced diffusion,1,2 which promises some advantages compared to conventional methods. Only the irradiated areas are doped. Using pulsed lasers, these areas are heated for a short time in which diffusion can take place. Due to rapid cooling, very high nonequilibrium concentrations of dopants can be incorporated as active donors or acceptors in a thin layer.

Fresnel zone plates which are used as imaging lenses for soft x-rays are required to have high resolution, high efficiency, and low distortions. In terms of practical realisation, this means smallest possible widths of the outer zones, high aspect ratios of the absorber rings, and a positional accuracy of the structures to a fraction of the outer zone width. Additionally, the absorptance of the membranes carrying the zone plate has to be minimized.

Microzone plates have been fabricated with the aid of a 100- keV electron beam lithography system. The system has been designed for generating structures with lateral dimensions of less than 100 nm. The particular demands on high resolution, high efficiency imaging Fresnel zone plates and the resultant problems concerning lithography and pattern transfer are discussed. We show a step-by-step improvement of fabricated microzone plates with an outermost zone width of 50 nm. A thin titanium intermediate layer is used as a stable mask to generate ion-milled gold absorber rings with very steep walls. The zone plates have been tested by imaging one another in an x-ray microscope and ave been compared to the image obtained with the holographically fabricated MZP3 microzone plate from Gottingen.

A semiconductor Anti-Stokes light convertor consisting of six layers (p-GaAs, n-GaAs, n-Ga x Al 1−x As, p-Ga y Al 1−y As, p-Ga x Al 1−x As, p-GaAs) has been fabricated using liquid phase epitaxy from Ga-rich melts. The n- and p-type GaAs forms a photodiode, which is integrated with a GaAlAs light emitting diode. Avalanche multiplication of photoexcited carriers is used to increase the LED driving current and thus the total conversion efficiency of the device.

An electronic analog model simulating the behaviour of diodes with pin-structure switched from forward to reverse bias is presented. Diodes with a lightly doped middle-region are used as power rectifiers, microwave modulators and step recovery diodes. Under the assumption of high injection and neutrality, the differential equations of the electrons and holes in the middle-region can be represented by a resistance-capacitance network. The conditions at the two boundaries ot the middle-region during the forward and storage period are simulated by constant current sources at the borders of the network. After the storage period the space-charge region of the pi-junction and somewhat later the space-charge region of the in-junction extend reducing the neutral part of the middle-region. This effect is simulated in the analog model by shortening the RC-network piece by piece. The currents at the moving borders of the network are reduced similar to the decreasing diode current during the decay period. Using this analog model the reverse recovery process of diodes with arbitrary doping profiles in the middle-region can be investigated. The model yields terminal properties and some quantities in the interior of the device, such as carrier densities and particle currents, as function of position and time. Results on the influence of forward and reverse currents, doping profile, width and carrier-lifetime in the middle-region are reported.

GaAlAs/GaAs phototransistors have been integrated with GaAlAs hetero-luminescent diodes to form an array. The high internal gain allows to construct an image converter with optical amplification. A high resolution structure is proposed.

The Double-Schottky-Interdigitated (DSI) photodetector has been shown to be a very-high-speed optical detector for λ < 0.9 µm. Its major drawback, a high dark current (1 µA at 10 V), has been overcome by quasi-ternary growth of the GaAs epitaxial layer, reducing the dark current by three orders of magnitude.

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. >

A new type of silicon PBT uses lateral selective low-pressure vapour-phase epitaxy to grow ridges with mushroom-like cross-sections leading to self-aligned gate and drain electrodes. Advantages are the lack of any etching damage encountered with etched-groove PBTs and high-temperature process compatibility. First experimental devices with bar widths of 1 –m exhibited transconductances of 7 mS/mm.

A two-step liquid-phase-epitaxial process has been used to fabricate widegap-emitter Schottky collector transistors. After the growth of the first two epitaxial layers the sample has been structured and then overgrown in a second run. In that way a pn homojunction in the widegap material (InP) underneath the extrinsic base-emitter region and a pn heterojunction under the collector have been formed. First transistors fabricated show a current gain of 10 in the common-emitter configuration.

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.

Fresnel zone plates have been fabricated by electron‐beam lithography using a modified scanning transmission electron microscope. These microzone plates are designed to work as imaging elements in an x‐ray microscope. To achieve zone plates that are free of distortions, the deflection field of the lithography system has been calibrated by the aid of externally generated reference marks. Microzone plates with a minimum linewidth of 20 nm have been written into polymethylmethacrylate and etched into a 15‐nm‐thick titanium layer. Two methods of transfer into a gold absorber layer have been used, namely sputter etching of the gold layer with a reactively ion etchedtitanium mask, and electroplating of gold using a suitable trilevel resist system. By these techniques, Fresnel zone plates with 100 zones, a width of the outermost zones of 50 nm, and a thickness of the gold absorber layer of 80 nm have been fabricated. Imaging experiments have been performed at the electron storage ring BESSY in Berlin, and the results have been compared with images obtained by holographically fabricated zone plates.

GaAs/GaAlAs double heterojunction I2L inverters with a vertical pnp current source were fabricated by ion implantation and Zn-diffusion into LPE structures. The current gain of the upside-down-operated double heterojunction npn transistor has been improved by a factor of two compared to the gain of the npn transistor of the otherwise similar structure. In addition, the wide-gap junction pnp transistor gives a solution to the critical switch-on problem which can occur when a wide-gap emitter transistor is used for the switching transistor.

A novel gate fabrication technique useful for MESFETs is presented. The gates have submicrometre dimensions with an extremely low ohmic resistance and are used for self alignment. Simple optical projection lithography and electroplating techniques are needed. The resulting gates have proved to be mechanically strong.

A Schottky contact photodiode on p-type GaInAs for application at λ=1.3–1.6 μm has been fabricated and tested. The coaxial type device shows an external quantum efficiency of 19% at λ=1.27 μm, and rise and fall times of less than 15 ps.

A Ga1-xAlxAs-GaAs heterostructure phototransistor has been manufactured and tested. The device is an n-p-n structure employing the ‘wide-gap-emitter’ effect. High internal current gain (>2000) has been achieved.

A hybrid light amplifier consisting of a GaAs-GaAlAs widegap phototransistor as light detector and a d.h. laser as light emitter has been realised. Amplification up to 25 dB has been achieved. Fastest turn-on and turn-off times were 16 ns and 24 ns, respectively. A monolithically integrated amplifier structure is proposed.

In the above paper, Akello et al. describe a method for experimental determination of the parasitic of microstrip-transistor packages, based on a resonance principle. A different method of measuring small reactances and susceptances, also permitting the determination of transistor-package elements based on time-dornain techniques, is given by Piller in [1]. This method avoids the difficulties resulting from critical coaxial to microstrip transitions.

A GaAlAs/GaAs heterojunction bipolar transistor has been developed and tested. A double base structure was adopted to facilitate critical selective etching problems. An emitter-collector breakdown voltage VCEO as high as 80 V was achieved. Maximum frequency of oscillationfmax of 850 MHz and a cutoff frequency fT of 1.6 GHz were realised. The current-gain/temperature curve shows that the transistor can be operated at temperatures up to 350°C.

Hot electron camel transistors have been fabricated for the first time in GaInAs. The camel structures were grown by MOCVD. The thickness of the base layer is 40 nm, the emitter barrier height is 0·55 eV, the collector barrier height is 0·25 eV, and the base transport factor is 0·6 at room temperature.

Photoconductive detectors with rise times less than 10 ps have been made from GaAs grown by laser-stimulated MOCVD. The growth temperature was 450°C, and laser pulse energy and pulse repetition frequency were 120 mJ and 10 Hz, respectively.