Effects of laser irradiation of GaAs observed by d.l.t.s.

A Q-switched ruby laser has been used to heat-treat vapourphase-epitaxial (v.p.e.) GaAs. The characteristic A-centre, a deep trapping level at 0.83 eV, is removed using a laser pulse of energy density 0.3 J cm?2. Trapping levels are observed using deep-level transient spectroscopy (d.l.t.s.).     

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.     

GaAs-GaAlAs anti-Stokes light convertor

A multilayer heterojunction device has been manufactured and used for efficient anti-Stokes light conversion. The device consists of six layers: p GaAs, n GaAs, n GaxAl1?xAs, p GayAl1?yAs, p GaxAl1?xAs and p GaAs, essentially forming a GaAs photodiode coupled with a GaAlAs l.e.d. Avalanche multiplication of photoexcited carriers is used to increase the l.e.d. driving current.     

GaAs m.e.s.f.e.t.: a high-speed optical detector

The application of a GaAs m.e.s.f.e.t. as a high-speed optical detector has been investigated and compared with the result of a fast a.p.d.     

Direct modulation of d.h. GaAlAs lasers with GaAs m.e.s.f.e.t.s

GaAs m.e.s.f.e.t.s are used to directly modulate d.h. GaAlAs lasers with a 200 Mbit/s pseudorandom, return-to-zero bit stream. The detected light pulses have 100% modulation depth, no significant intersymbol interference, 40 mW of peak power and risetimes and falltimes of 240 ps for a halfpower width of 280 ps.     

Laser annealing of low dose Se-implanted GaAs studied by d.l.t.s.

Deep level transient spectroscopy (d.l.t.s.) has been applied to the study of deep levels in GaAs following post-implantation annealing using a Q-switched ruby laser. High concentrations (> 1015 cm?3) of deep trapping levels are observed in the laser melt region using a forward-bias voltage pulse.     

Normally-off m.e.s.f.e.t. with fast switching behaviour

Normally-off m.c.s.f.e.t.s, fabricated on an insulating GaAs substrate with a vapour-phase-grown double layer (n?/n), showed a d.c. characteristic with a good saturation range and a switching response of 35 ps risetime.     

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.     

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.     

GaAs f.e.t.s with graded channel doping profiles

Graded-channel GaAs f.e.t.s with the carrier concentration decreasing from the substrate?epitaxial interface outwards are observed to exhibit more linear d.c. transfer characteristics, higher reverse gate breakdown voltages and lower 3rd-order intermodulation products than f.e.t.s fabricated from companion slices with uniform or flat doping profiles.     

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.     

Effect of Johnson noise on l.s.a. oscillators

The r.m.s. electron-density fluctuations (Johnson noise) within the GaAs of l.s.a. oscillators are shown to be about 10% of the mean density. The effect of these fluctuations is determined by an analytic calculation of l.s.a.-oscillator efficiency (similar to that of Bott and Hilsum, 1967). The specification of the velocity/field characteristic of conduction electrons in GaAs in an analytical form, which separates the importance of peak/valley ratio and negative differential mobility, permits an indication of the optimum form of the characteristic for the l.s.a. mode. The calculated efficiencies are somewhat smaller than those of previous calculations.     

Wide-bandwidth high-radiance gallium-arsenide light-emitting diodes for fibre-optic communication

High-radiance GaAs l.e.d.s with 3 dB modulation bandwidths exceeding 500 MHz have been fabricated from p-n junction layers prepared with very high zinc acceptor doping levels. This development will permit the use of l.e.d.s in near-gigahertz or gigabit/s optical-fibre communication links.     

Mobility, transit time and transconductance in submicrometre-gate-length m.e.s.f.e.t.s

Two-dimensional simulations of submicrometre-gate-length m.e.s.f.e.t.s of Si, GaAs and InP show that device transit time and transconductance depend more on high-field diffusion constant and the shape of the velocity/field characteristic than on low-field mobility. Reasonable InP devices have shorter transit times and higher transconductances than GaAs devices, and for certain device parameters these figures of merit can be almost the same for Si and GaAs devices.     

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.     

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.     

GaAs m.e.s.f.e.t. prepared by organometallic chemical vapour deposition

GaAs m.e.s.f.e.t.s with gate dimensions of 1.5 ?m × 300 ?m were fabricated in the epitaxial layers grown by organometallic chemical vapour deposition (o.m.c.v.d.) technique. The average saturation velocity in the channel was deduced to be 1.3 × 107 cm/s and is equal to that of epitaxial layers grown by AsCl3 chemical vapour deposition (c.v.d.). The velocity degraded region was confined to within about 350 ? of the interface. A gain of 10 dB and a noise figure of 3 dB with an associated gain of 5.5 dB at 8 GHz were measured.     

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.     

Low-noise microwave f.e.t.s fabricated by molecular-beam epitaxy

The growth of m.b.e. GaAs suitable for f.e.t. fabrication is reported. The m.b.e. structure consists of an n+ = 2.5×1018 cm?3 contact layer on top of an n+ = 3.5×1017 cm?3 active layer. Using this material, f.e.t.s. have been fabricated that have a minimum noise figure of 1.5 dB with an associated gain of 15 dB at 8 GHz. These are the best results yet reported for low-noise m.b.e. GaAs f.e.t.s.