X-band performance of GaAs power f.e.t.s

The results of X-band measurements on GaAs power f.e.t.s are reported. These devices are fabricated with a simple planar process. Devices with output powers of 1 W or more at 9 GHz with 4 dB gain have been fabricated from more than a dozen slices. The highest output powers observed with 4 dB gain are 1.78 W at 9 GHz and 2.5 W at 8 GHz. Devices have been operated with 46% power-added efficiency at 8 GHz.     

GaAs power f.e.t.s with electron-beam-defined gates

The fabrication of GaAs power f.e.t.s having 1 ?m electron-beam-defined gates with 4800 ?m total gatewidth is described. The microwave performance at X-band is compared with that of conventionally defined devices having 2 ?m gate lengths.     

GaAs power f.e.t.s with semi-insulated gates

GaAs semi-insulated-gate f.e.t.s (s.i.g.f.e.t.s) have been fabricated by Ar+ bombardment in the gate region. The d c. characteristics and microwave performance are compared with those of conventional power m.e.s.f.e.t.s fabricated from the same slice. Up to 2.9W output power with 4dB gain has been obtained from s.i.g.f.e.t. devices at 8 GHz.     

Performance of GaAs power m.e.s.f.e.t.s

Power performance results at 4 GHz are summarised for GaAs m.e.s.f.e.t.s ranging in size from 4 to 16 mm gate periphery. A double-chip 16 mm unit operated at 24 V source-drain bias produced 13.5 W with 3 dB gain and 10.7 W with 8.1 dB gain. Although lack of perfect power and gain scaling is observed, the degradation in output power of the 16 mm devices was only 1 dB compared to the smaller devices.     

Performance of self-oscillating GaAs m.e.s.f.e.t. mixers at X-band

A new mode of m.e.s.f.e.t. operation, the self-oscillating mixer is reported. Conversion gains of up to 2 dB at 10 GHz and noise figures as good as 15 dB have been demonstrated by using a simple circuit.     

Low-noise GaAs m.e.s.f.e.t.s

GaAs m.e.s.f.e.t.s with optimum noise figures of 1.6 dB at 6 GHz have been fabricated by projection photolithography. An equation has been developed for the calculation of optimum noise figure which gives good agreement between calculated and measured values.     

GaAs power m.e.s.f.e.t.s. with a graded recess structure

A new recess structure device was developed to improve the field distrubution and therfore the performance of GaAs power m.e.s.f.e.t.s. The linear gain and the output power were improved by 1?2 dB for this structure. The highest output powers obtained are 15 W with 4 dB associated gain at 6 GHz, and 4.3 W with 3 dB associated gain at 11 GHz.     

Dual-gate m.e.s.f.e.t. self-oscillating X-band mixers

GaAs dual-gate m.e.s.f.e.t.s have been successfully used as self-oscillating down-convertors in X-band. A single device replaces the preamplifier, mixer and local oscillator. The best conversion gain achieved by mixing from 10 GHz down to 1 GHz was 12 dB. The input (gate 1) to output (drain) port isolation amounted to 16 dB. Slug-tuner and `disc?-resonator circuits were tested and showed comparable gain and noise performance. Best d.s.b. noise figures of 5.5 dB could be realised at an i.f. of 1 GHz with an associated conversion gain of 4 dB.     

Light-induced effects in GaAs f.e.t.s

It is shown theoretically and experimentally that the variations of the d.c. and dynamic properties in a GaAs f.e.t. when a light beam strikes the transistor's gate can be accounted for by an appropriate change in the gate-junction equivalent built-in voltage. A simple relationship connects this change with the variations of the light intensity.     

Performance of selenium-ion-implanted GaAs f.e.t.s

Selenium-ion-implanted GaAs f.e.t.s have given minimum noise figures as low as 3·4 dB and maximum available gains of at least 10 dB at 10 GHz. The devices do not appear to suffer from short-term drift problems, and have greater device-characteristic uniformity and reproducibility than epitaxial f.e.t.s.     

Performance of sulphur-ion-implanted GaAs f.e.t.s

GaAs f.e.t.s have been produced by sulphur-ion implantation that give optimum noise figures as low as 4.6 dB at 10 GHz and maximum available gains of greater than 10 dB at 10 GHz. A considerable degree of uniformity among the devices is observed.     

GaAs f.e.t.s with silicon-implanted channels

Field-effect transistors with channel doping profiles fabricated by the implantation of silicon ions into high-resistivity vapour phase epitaxial GaAs have given noise figures of 2.9 dB with an associated gain of approximately 5 dB at 10 GHz. Similar measurements on F.E.T.S fabricated in an identical manner, except for the channel fabrication, where silicon ions were implanted directly into a Cr-doped semi-insulating GaAs substrate, have resulted in nose figures typically 1 dB higher.     

Substrate conduction in GaAs m.e.s.f.e.t.s

Substrate currents in a gateless GaAs m.e.s.f.e.t. have been measured at d.c, 0.9 MHz and 2 GHz. The results are consistent with the assumption of substrate conduction at high frequencies and active-layer conduction alone at low frequencies.     

Avalanche noise in GaAs m.e.s.f.e.t.s

Instabilities in the d.c. characteristics of GaAs m.e.s.f.e.t.s for drain to source voltages greater than 4 V. believed to be due to reloading of traps in the interface between active layer and bulk material, or gunn-domain formation, seem to have their origin in avalanche breakdown of the back diode under the drain contact. Microplasma switching, vertical to the active layer, strongly modulates the drain current producing large broadband noise power.     

High peripheral power density GaAs f.e.t. oscillator

Peripheral power density (p.p.d.), i.e. the output power per Unit gate width is defined as a figure of merit for GaAs f.e.t. oscillators. An X-band oscillator circuit using series and shunt feedback is described and its performance characteristies indicated. It is shown that this GaAs f.e.t. oscillator circuit configuration has the highest peripheral power density.     

Electrical traps in GaAs microwave f.e.t.s

Described is a rapid, sensitive technique for determining the activation energies for electron traps present in the channel of GaAs microwave field-effect transistors. The measurements can be made directly on the f.e.t.s. Taken together with systematic variation of growth procedures, the method can be applied toward identification and elimination of the traps.     

Capacitor-coupled logic using GaAs depletion-mode f.e.t.s

A new method of interconnecting depletion-mode GaAs f.e.t. logic stages, using capacitive coupling, eliminates the need for a negative power supply and is more tolerant of processing spreads, particularly of pinch-off voltage. The technique may be combined with conventional level shifting, operating at very low current. The use of capacitance may be extended to achieve clocked dynamic data storage with very low power dissipation.     

Effects of capacitance at crossover wirings in power GaAs m.e.s.f.e.t.s.

Power GaAs f.e.t.s. with an air-bridge crossover were compared with those of SiO2 crossover to find the effect of the capacitance at the crossover points. The capacitance of SiO2 crossover points is much smaller than that of the gate pad or the gate busbar in power GaAs f.e.t.s, and deterioration of the microwave performance due to that capacitance is negligible.     

High-efficiency GaAs m.e.s.f.e.t. amplifiers

High-efficiency c.w. amplification with GaAs m.e.s.f.e.t.s under class-B conditions has been demonstrated. Power added efficiencies as high as 68% at 4 GHz and 41% at 8 GHz have been achieved. Two-tone tests were carried out at 4 GHz. The power added efficiencies at the 3rd-order intermodulation levels of ?20, ?25 and ?30 dB were 49, 40 and 35% respectively.     

Relationship between power added efficiency and gate-drain avalanche in GaAs m.e.s.f.e.t.s

Pulse avalanche measurements in the transistor three-terminal configuration reveal a correlation between pulse gate-drain avalanche and power added efficiency. This result, in conjunction with earlier work, points to simple design principles that can be used to maximise efficiency.