Since 1970, InP has been developed as a material for microwave oscillators and amplifiers, with most interest to date being taken in transferred-electron devices. the physics of electron transport and of transferred-electron oscillators is reviewed; the features of greatest practical significance are the high potential oscillator efficiency set by the peak-to-valley ratio, which is approximately 3·5, of the velocity/field curve; studies of cathode-contact effects which have led to oscillator efficiencies over 20% and the observation of limited-space-charge-accumulation (l.s.a.) mode operation. Consideration is also given to other less developed InP microwave components, including transferred-electron small-signal amplifiers which have given noise measures of 8 dB at 15 GHz, and field-effect transistors for which encouraging preliminary results have been obtained.

Indium phosphide: a semiconductor for microwave devices

A numerical method for designing notch doping profiles for transferred-electron devices is presented. The profile is calculated to be consistent with a given uniform field in the active region and carrier density at the end of the notch. An example of this method is done for InP using a computer model which includes relaxation effects. For this example it is found that the required notch doping is p type and the active region doping is slightly nonuniform due to relaxation effects.

Design of cathode doping notches to achieve uniform fields in transferred-electron devices

A displaced Maxwellian approach which includes relaxation effects is used to simulate small- and large-signal InP transferred-electron amplifiers operating in Ka -band. The devices considered are short-circuit stable; that is, they have a subcritical doping-length product. The performance of amplifiers having the usual n+-cathode contacts, and p-type notch-cathode contacts designed to produce a uniform electric field, are compared. It is found that the notch contacts have a moderate influence on small-signal characteristics, and a profound influence on large-signal performance. Small-signal bandwidths of 65 percent are predicted for both types of contacts. The saturation efficiency of amplifiers, biased at three times threshold, is much higher for the notch-contact device with values near 5 percent being predicted. The nonlinearity of the large-signal gain characteristic is shown to vary greatly as the frequency deviates from the optimum value.

Computer simulation of InP transferred-electron amplifiers for Ka-band

10-W p-n junction GaAs IMPATT diodes with MTTF more than 10/sup 6/ h, have been developed. Using these diodes, amplifiers of 5-W output power, 10-dB gain, 17-percent efficiency, 150-MHz bandwidth, and 80-dB signal-to-noise ratio (S/N ratio) have been constructed.

High Power GaAs IMPATT Amplifier

Performance results and design considerations are presented for an all solid-state Ku-band power amplifier which is feasible for use in PM communication systems for airborne or spacecraft transmitter applications. Design emphasis is placed on high power, and high efficiency operation as well as on compact amplifier construction. A six-stage GaAs FET preamplifier and a driver and balanced power amplifier utilizing GaAs IMPATT diodes operating in the injection locked oscillator mode are discussed. For high power and efficiency Schottky-Read IMPATT's with Iow-high-low doping profiles are employed. For improved reliability the IMPATT's incorporate a TiW barrier metallization to retard degradation of the IMPATT's. Results of accelerated life testing of the IMPATT devices are also presented.

A 4-W 56-dB Gain Microstrip Amplifier at 15 GHz Utilizing GaAs FET's and IMPATT Diodes

GaAs IMPATT devices using p+–n and p–n junctions with hi–lo and lo–hi–lo structures were investigated. A maximum efficiency of 26.8% and a maximum peak power of 12.8 W with 25% efficiency have been observed in the X band. A median life of 107 h is predicted for a 237°C junction temperature.

S. I. Long

Papers

High-efficiency p--n junction GaAs IMPATT devices

Low noise GaAs Gunn amplifier structures for K and Ka-band