Walter Kellner

A two-phase CCD on GaAs with 0.3-µm-wide electrode gaps

A two-phase GaAs Schottky-barrier CCD with 32 electrodes, a gate length of 4 µm, and interelectrode gaps of 0.3 µm was fabricated and tested. The unidirectional charge flow is obtained by using a stepped-electrode configuration realized by etching and angle evaporation. First measurements show the feasibility of this principle which greatly simplifies CCD operation at very high frequencies.

Three-phase GaAs Schottky-barrier CCD operated up to 100-MHz clock frequency

GaAs CCDs with 5-µm electrodes were fabricated using a process fully compatible to MESFET integrated circuits. The devices were operated at clock frequencies from 100 kHz to 100 MHz. The transfer inefficiency was found to be ≈ 1 × 10-2in the frequency range from 100 kHz to 30 MHz. This is due to an incomplete charge transfer caused by interelectrode gaps larger than the layer thickness.

A Schottky-barrier CCD on GaAs

Because of its high electron-mobility GaAs is a promising semiconductor for high speed CCDs. To avoid the problems encountered with MIS-structures (e.g., high surface state density, frequency dependent C(U)-characteristics) a CCD with Schottky-contacts was proposed (Schuermeyer 1972). To our knowledge no operating GaAs-CCD has been reported until now. Basically the structure of our CCD is that of a GaAs MESFET with a sequence of gates. During operation, electrons are injected from the source into the depleted n-type layer. By proper biasing of the Schottky-gates the injected charge is stored or transferred along the interface between active layer and substrate. The signal is detected by use of a monolithically integrated read-out MESFET-amplifier. A three phase-four stage CCD was fabricated on sulphur-implanted active layers on semi-insulating GaAs. The ohmic contacts consist of a layer sequence of GeAuCrAu. CrAu-Schottky-contacts with 6.5 µm in length and 200 µm in width were used. Interelectrode spacing was 1.5 µm. SiO2was sputter-deposited for electrode crossover and passivation. Operation of the CCD at 500 kHz showed correct single pulse and step response. The number of stages were too small for accurately measuring the transfer inefficiency, which is estimated to be smaller than 5.10-3. Elements with 8 or 16 stages for determining the transfer inefficiency and the maximum frequency of operation are presently under investigation.

Current gain recovery in silicon nitride passivated planar transistors by hydrogen implantation

During deposition of silicon nitride, the low-current h<inf>FE</inf>of silicon planar transistors decreases. When the nitride layer completely seals the oxide from the ambient, the initial value of h<inf>FE</inf>cannot be restored by annealing at 500°C in forming gas. To eliminate this difficulty, hydrogen ions have been implanted at an energy of 70 keV and at doses varying from 1.10¹³to 1.10¹⁶cm^-2through the nitride into the oxide. Optimum h<inf>FE</inf>recovery has been obtained with implantation at a dose of 3.10¹⁵cm^-2followed by a radiation damage annealing at 400-500°C in dry nitrogen.

Microwave field-effect transistors from sulphur-implanted GaAs

Sulphur implantation into semi-insulating GaAs has been used to fabricate 1,5µ-gate-MESFETs showing microwave gain equivalent to epitaxial FETs (MAG = 10 dB at 10 GHz) but higher noise. Room temperature implantation of S at an energy of 30 keV and a dose of 5.10¹²cm^-2sputtered SiO<inf>2</inf>and Si<inf>3</inf>N<inf>4</inf>as encapsulants and heat treatments from 820 to 900°C have been used. Electrical activation was found to, depend critically on the substrate material. Si<inf>3</inf>N<inf>4</inf>-encapsulation gave slightly higher electrical activation than SiO<inf>2</inf>.

Design considerations for planar Schottky barrier diodes

Abstract The cut-off frequency of the simplest planar Schottky diode on a uniformly doped n-layer of GaAs is derived. The theoretical results are given as functions of doping concentration and layer thickness with the specific contact resistance as parameter. An improved planar diode structure is presented with several short Schottky contact fingers connected in parallel. Experimental values ranging from 100 to 300 GHz agree with the calculated values when parasitic capacitances are taken into account.

Ausblick: Monolithisch integrierte Schaltungen auf GaAs

Monolithisch integrierte Schaltungen auf GaAs haben in den Jahren seit 1980 einen auserst raschen Aufschwung genommen. Dieses Kapitel kann daher nur einen kurzen uberblick uber den bis jetzt erreichten Stand (1988) bei analogen und digitalen Schaltungen geben. Ausfuhrliche Informationen uber GaAs-IS sowie uber neueste Entwicklungen (optoelektronische integrierte Schaltungen, Schaltungen auf anderen III-V-Halbleitern als GaAs oder auf Schichtfolgen) sind z.B. in Tagungsbanden zu finden: GaAs IC Symposium (jahrlich seit 1979), International Solid-State Circuits Conference, Symposium on GaAs and related compounds.

Stabilität und Zuverlässigkeit von GaAs-MESFET

Im Vergleich zu Bauelementen auf Silizium und Germanium ist der GaAs-MESFET ein relativ junges Bauelement. 1975 kamen die ersten kauflichen Kleinsignal-MESFET auf den Markt. Diese ersten Muster zeigten zwar schon gute Hochfrequenzeigenschaften, ihre Stabilitat und Zuverlassigkeit liesen aber noch viele Wunsche offen: Manche Transistoren “starben” schon beim Einbau in die Schaltung, andere zeigten bereits nach kurzer Betriebszeit Veranderungen in ihren Eigenschaften. Obwohl mittlerweile feststeht, das der GaAs-MESFET durchaus die Zuverlassigkeit von Bauelementen auf Silizium erreicht (vgl. Abschn.6.3), sind einige der im folgenden erwahnten Probleme noch nicht gelost.

Ternäre und quaternäre Halbleiter für Hochfrequenz-FET

Das elektronische Verhalten von Halbleiterbauelementen ist eng verknupft mit den Eigenschaften des Halbleitermaterials, in welchem sie realisiert werden. Parasitare Grosen, die ihren Ursprung im Design und in nicht optimalen Herstellungsbedingungen haben, verfalschen die erzielbaren Ergebnisse. Letztlich sind es aber die Transporteigenschaften und die Bandstruktur des Halbleitermaterials, welche die bestimmenden Faktoren darstellen.

A Double Balanced Mixer for TV Tuners based on GaAs-FETs

A double balanced mixer and amplifier was built with GaAs ICs. Results: (1) Constant conversion gain of 12 ± 2 dB over the entire TV-band (50-900 MHz). (2) Good linearity for large signals. (3) Low noise figure (#8 dB).