n-channel inversion-mode InP m.i.s.f.e.t.

Capacitance/voltage and m.i.s.f.e.t. inversion-mode f.e.t. data are reported for p-type InP. It is shown that the surface of this material appears to be inverted at zero gate bias and that good inversion-mode (normally-off) device behaviour is possible.     

New n-channel m.o.s.f.e.t.s

By using plasma c.v.d. and lift-off, an n-channel m.o.s.f.e.t. with effective channel length of 0.4 ?m has been fabricated. Its main fabrication processes and obtained electrical characteristics are described.     

Microwave gain from an n-channel enhancement-mode InP m.i.s.f.e.t.

A power gain of 14 dB at 1 GHz has been demonstrated in an enhancement-mode m.i.s.f.e.t. constructed on an Fe-doped semi-insulating InP substrate. The same device also exhibits well behaved gain characteristics at low frequencies.     

n-channel formation on semi-insulating InP surface by m.i.s.f.e.t.

InP m.i.s.f.e.t.s using Fe-doped semi-insulating material surface have been fabricated. The devices, composed of sulphur-diffused n-type source and drain and c.v.d. Al2O3 gate insulator, exhibited n-channel normally-off behaviour and a source drain capacitance two orders of magnitude smaller than that of p-InP m.i.s.f.e.t.s with the same dimensions.     

InP/Al2O3n-channel inversion-mode m.i.s.f.e.t.s using sulphur-diffused source and drain

InP metal-insulator-semiconductor field-effect transistors (m.i.s.f.e.t.s) have been fabricated using c.v.d. Al2O3 as the gate insulator and the sulphur-diffusion process for source and drain. The n-channel inversion-mode device exhibits normally off behaviour. A maximum d.c. transconductance gm of 10 mS (87 mS/mm of gate width) has been obtained.     

CdTe/Langmuir-film m.i.s. structures

Langmuir films based on cadmium stearate have been successfully deposited on to the surface of p-type CdTe. The measured C/V curves show, for the first time, the accumulation, depletion and weak-inversion regions typical of an ideal device. The G/V curves show a sharp peak in the depletion region at high frequencies which is thought to be due to losses at interface states. An initial estimate of the density yields an average value of 1011 states cm?2.     

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.     

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.     

High-speed 1 ?m GaAs m.e.s.f.e.t.

By minimising parasitic series resistances, a GaAs m.e.s.f.e.t. with 1 ?m gate length was fabricated, possessing the highest known r.f. power gain, measured up to 18 GHz, for GaAs m.e.s.f.e.t.s.     

Micrometre-gate m.e.s.f.e.t.s on laser-annealed polysilicon

Schottky-barrier field-effect transistors (m.e.s.f.e.t.s) have been fabricated on uniformly doped laser-annealed polycrystalline silicon deposited on a silicon nitride insulator. The devices, which had aluminium Schottky-barrier gates and diffused n+ sources and drains but nonoptimised channel profiles, had about 65% the gm values of similar but optimised devices made on s.o.s. layers. Performance of these devices is considered adequate for certain innovative integrated-circuit technologies.     

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.     

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.     

Multi/demultiplexing in Gbit/s range using dual gate GaAs m.e.s.f.e.t.s

Multiplexing from 1 to 2 Gbit/s and corresponding demultiplexing from 2 to 1 Gbit/s including clock regeneration and pulse width reduction has been performed using dual gate GaAs m.e.s.f.e.t.s. Circuits and time behaviour of input, clock and output signals are shown.     

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.     

Bit synchronisation in Gbit/s range using dual gate GaAs m.e.s.f.e.t.s

Bit synchronisation at 1 and 2 Gbit/s including pulse width reduction is achieved using dual gate GaAs m.e.s.f.e.t.s. Circuits and time behaviour of input-, clock- and output signals are shown.     

Modelling the m.e.s.f.e.t. output nonlinearity

Conditions governing the modelling of transductance and drain-conductance nonlinearities from measured data are investigated. A simple representation for regions close to pinch-off, corresponding to mixer operation, is obtained. Results of the modelling are compared to measurements on a typical 1 ?m gate length m.e.s.f.e.t.     

Two-dimensional electron gas m.e.s.f.e.t. structure

The first m.e.s.f.e.t. structure is reported in which the channel near pinch-off is occupied by a two-dimensional electron gas accumulated at the interface of a GaAs(N)-AlxGa1?xAs(N) heterojunction. Experimental data are in good agreement with theoretical calculations.     

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.     

High-yield self-alignment method for submicrometre GaAs m.e.s.f.e.t.s

A high-yield self-alignment technique for submicrometer GaAs m.e.s.f.e.t.s is described. This method allows the production of submicrometre gate lengths and source-drain spacings by means of standard contact photolithography without requiring a particularly fine geometry on the masks. A 0.5 ?m long gate and a source-drain spacing of 2 ?m were obtained.