Trap localisation in the active layer of GaAs microwave f.e.t.s

The localisation of traps in the active layer of GaAs microwave m.e.s.f.e.t.s has been effected for two different epitaxial materials. The method used in this work was a transient measurement of source-drain voltage associated with a simple theoretical model. Our results indicate that electron traps are localised in the bulk of the epilayer whereas hole traps are localised at the epilayer/buffer-layer interface.     

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.     

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.     

Tungsten/gold gate GaAs microwave f.e.t.

Preliminary results on the performance of a W/Au gate GaAs f.e.t. having T-type gate cross-section are reported. The Au overhang on the W gate can be used to self-align the source and the drain with respect to the gate, which can be used to achieve submicrometre gate dimensions rather easily. An f.e.t. with 0.7 ?m gate length and 140 ?m gate periphery exhibited a measured maximum available gain (m.a.g.) of 14 dB at 8 GHz, Experiments on the W Schottky diodes indicate that the leakage current, instead of degrading, is actually reduced by annealing at high temperature in a H2 atmosphere for 10 min.     

Modelling of microwave GaAs f.e.t. in common-gate operation

The common-source and common-gate equivalent circuits of GaAs f.e.t. at microwave frequencies are established and used to simulate the variations of gain and noise figure with frequency. The results obtained explain why the experimental minimum noise figure and source admittance in the common-gate configuration are different from the theoretical expectations based on low-frequency calculations.     

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.     

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.     

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.     

Ion-implanted GaAs X-band power f.e.t.s

Active layers for GaAs power f.e.t.s have been produced by Si implantation into Cr-doped substrates followed by a simple proximity-annealing technique. Devices fabricated on these layers have up to 1.05 W/mm gate width at 10 GHz. This performance is equal to that of epitaxial devices.     

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.     

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.     

New structure of enhancement-mode GaAs microwave m.o.s.f.e.t.

This letter proposes a new feasible device structure of an enhancement-mode GaAs deep-depletion m.o.s.f.e.t. as an attractive alternative to the junction-gate f.e.t.s and describes its microwave properties. The device has been fabricated on a high-resistance epitaxial n?-layer by simple readily available technology without requiring the sophisticated control of the channel thickness needed for the conventional junction-gate f.e.t.s. The 'normally-off nature of the device can be explained on the basis of the substrate space-charge region extending over then?-layer. The microwave performance of the device can be favourably compared with that of currently achievable junction-gate normally-off f.e.t.s. Unilateral gain drops to zero at a frequency slightly above 7 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.     

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.     

Low-frequency noise in GaAs Schottky-gate f.e.t.s.

Measurements of the low-frequency noise in GaAs Schotty-gate f.e.t. channels have been performed from 10 Hz to 0.5 MHz between ?120 and +21 °C. Diffusion and recombination noise sources appear to be predominant at low temperatures for low-power-level conditions. Nous avons entrepris la mesure du bruit basse fréquence prenant naissance dans le canal des f.e.t. à l'arséniure de gallium pour des fréquences allant de 10 Hz à 0. 5 MHz et une température comprise entre ?120 et +21 °C. Nous avons mis en évidence que pour de faibles puissances dissipées les sources de bruit principales à basse température ont pour origine des phénomènes de diffusion et de génération recombinaison.     

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.     

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.     

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.     

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.     

Modelling of Gunn-domain effects in GaAs m.e.s.f.e.t.s

GaAs m.e.s.f.e.t. [S22] values larger than unity have been measured from 1 to 10 GHz in the region where the ID/VD curves display a negative slope. An explanation of this phenomenon is proposed in terms of Gunn-domain formation. An equivalent-circuit model which includes this effect is presented and discussed.