Medium-power GaAs field-effect transistors

Results on medium-power GaAs m.e.s.f.e.t.s. are described. Output powers as high as 300 mW at 9 GHz at 1 dB gain compression with a linear gain of 5.2 dB and drain efficiency of 30% have been obtained with single-cell m.e.s.f.e.t.s. At 4 GHz, a power output of 665 mW at 1 dB gain compression, a linear gain of 8 dB and a drain efficiency of 44.5% were realised with a 3-cell m.e.s.f.e.t. Two-tone intermodulation characteristics at 4 GHz are also described. A major innovation has been the use of a high-resistivity chromium-doped epitaxial GaAs buffer layer to isolate the device active region from the bulk-grown substrate.     

GaAs field-effect transistors with ion-implanted channels

Schottky-barrier-gate n channel depletion-mode field-effect transistors have been fabricated in GaAs by the use of sulphurion implantation directly into semi-insulating Cr-doped substrates to produce the channel. This technique eliminates the need for the growth of a thin epitaxial layer, as is usually done, and results in better uniformity of device characteristics over the wafer area. Performance of these devices at 1 to 12 GHz is described, and low-frequency characteristics are given.     

Novel microwave GaAs field-effect transistors

A technology is described for the fabrication of Schottky-barrier f.e.t.s with electrodes on either or both sides of a submicrometre thick single-crystal layer of GaAs. Preliminary d.c. and microwave results are given together with possible advantages of these novel f.e.t. structures.     

Reliability of power GaAs field-effect transistors

The first report on a comprehensive study of the reliability of power GaAs FET's with aluminum gates and silicon-nitride passivation is presented. A total of 265 standard 6-mm-wide devices has been aged under dc-bias conditions with and without RF drive at channel temperatures of 250, 210, and 175°C. One-million device-hours have been accumulated with no catastrophic failure. A very conservative estimate predicts that the failure rate for burnout at a maximum channel temperature in normal operation of 110°C would be below 100 FIT's. Degradation in the electrical parameters has been very slow even at 250°C channel temperature. It is estimated that the failure rate for gradual degradation at 110°C would be well below 100 FIT's and most likely lower than 10 FIT's. No deterioration in the properties of gates and ohmic contacts have been observed. Diagnostic characterization has revealed that gradual degradation in the sample devices is caused by deterioration in the channel material. There has been no noticeable difference in gradual degradation between devices aged with and without RF drive at the same channel temperature for more than 3000 h. The present study has already demonstrated that the power GaAs FET's used as the samples are very reliable.     

Ion-implanted microwave field-effect transistors in GaAs

Microwave field effect transistors have been fabricated in gallium arsenide by using sulfur ion implantation directly into semi insulating Cr doped substrates to produce the channel region, eliminating the need for growth of an epitaxial layer. This implantation method has been used to produce 0·25 μm thick, n-type layers with uniform thickness and carrier concentration, and carrier mobility ranging from 2410 to 3620 cm²/V sec in different samples. Because of the uniformity, FET's fabricated in these layers have exhibited reproducibility of transconductance and pinchoff voltage from device to device on a wafer to better than ±10 per cent. Cr doped GaAs of commonly available quality was found to be satisfactory for FET fabrication, although minimum Cr compensation is desirable to obtain highest mobility. S parameter measurements of microwave characteristics indicated a projected f_max = 20 GHz but transducer gain cutoff occurred at approximately 7 GHz because of impedance mismatch and package parasitics.     

Microwave field-effect transistors from sulphur-implanted GaAs

Sulphur implanation into semi-insulating Cr doped GaAs has been used to fabricate MESFETs with 1.5 μm gatelength showing microwave gain equivalent to epitaxial FETs (MAG = 9 dB at 10 GHz) but higher noise. Room temperature implantation of S at an energy of 30 keV and a dose of 5 × 10¹² cm^?2, sputtered SiO₂ and Si₃N₄ as encapsulants and heat treatments from 820 to 900°C have been used. Electrical activation was found to depend critically on the substrate material. Si₃N₄-encapsulation gave slightly higher electrical activation than SiO₂.     

Epitaxial GaAs p-n junction field-effect transistors

Structure and fabrication of single-gate GaAs p-n junction field-effect transistors is described. The devices employ n-type GaAs layers grown epitaxially on semi-insulating substrates of GaAs. Experimental devices indicate a cutoff frequency of approximately 2 GHz. Optimized device geometries promise operation at microwave frequencies as amplifiers and oscillators. Negative resistance oscillations above a field of approximately 3 × 10³V/cm have been observed.     

GaAs field-effect transistors by selective sulphur-ion implantation

GaAs field-effect transistors without a mesa structure have been fabricated by selective sulphur-ion implantation into Cr-doped GaAs substrates. The transconductance was 16 mS and the maximum oscillation frequency was 30 GHz.     

Frequency limits of GaAs and InP field-effect transistors

Monte Carlo calculations of electron transport in InP and GaAs short-channel field-effect transisters (FET's) show that a significant departure from the equilibrium velocity-field curve occurs in these devices. On the basis of these calculations, InP FET's should have high-frequency performance superior to that of GaAs FET's only for effective channel lengths in excess of 1.5 µ.     

Noise behavior of GaAs field-effect transistors with short gate lengths

The noise behavior of the GaAs Schottky-barrier gate field-effect transistor has been investigated theoretically and experimentally. It has been found that an additional noise source has to be taken into account in GaAs FET's biased in the pinchoff region: the intervalley scattering noise. This noise source has been investigated and a new transistor noise model is proposed. Measured and calculated noise figures show good agreement in the frequency range 2-10 GHz. It is shown that the influence of the intervalley scattering noise can be reduced by reducing the channel thickness, and that such devices show excellent gain and noise properties in the X band.     

Comparison of input offset voltage of differential amplifiers using bipolar transistors and field-effect transistors

A field-effect transistor (whether junction type or MOS type) has very high input impedance. For those who desire to achieve a higher input impedance, it is often asked `Why aren't FET pairs used as input stages and bipolar transistors used as output stages, since compatible FET and bipolar transistor monolithic structures have been developed?' This correspondence is a study of this question.     

Inverted GaAs/AlGaAs modulation-doped field-effect transistors with extremely high transconductances

Inverted GaAs/AsGaAs MODFET's with transconductances as high as 1810 mS/mm at 77 K and 1180 mS/mm at 300 K are fabricated using a self-aligned process. The devices have the gate-heterojunction interface spacing of only 100 Å, and the observed values of the transconductance are limited primarily by the source series resistance and by the gate current. The MODFET characteristics are interpreted using the charge control velocity saturation model which takes into account the gate current. The obtained results show a great potential of inverted MODFET's for ultrahigh-speed applications.     

CW oscillation characteristics of GaAs Schottky-barrier gate field-effect transistors

The CW oscillation characteristics of GaAs Schottky-barrier gate FET's have been examined at 10 GHz. The maximum output power of 41.2 mW and the maximum efficiency of 15.6 percent have been obtained for the GaAs FET with a gate length of 1.5 µm and an electrode width of 300 µm. The experimental results have shown that the GaAs FET possesses promising features for an oscillator application as well as an amplifier application.     

The performance of GaAs field-effect transistors as microwave mixers

The performance of Schottky barrier gate field-effect transistors (FET's) as single-ended microwave mixers at 3 GHz is described. An increase in dynamic range of approximately 10 dB over conventional diode mixers is reported although the noise figures of FET miters at present are higher than for diode mixers.     

X- and Ku-band internally matched packaged GaAs f.e.t.

The design and performances of medium-power X- and Ku-band internally matched GaAs f.e.t.s are reported. With input-output v.s.w.r. lower than 2 : 1 over more than 20% bandwidth in the X-band and l0% in the Ku-band, 50 and 200 mW two-stage cascaded amplifiers have been realised with no matching circuit outside the packaged f.e.t. and with only one power supply.     

Generation-recombination noise in the channel of GaAs Schottky-gate field-effect transistors

The low-frequency noise in GaAs m.e.s. f.e.t.s was measured continuously for temperatures varying from 80 to 310K. It presented distinct maxima, suggesting the presence of several g.r. processes. The shift of these peaks at different frequencies (500 Hz to 1 MHz) allowed us to obtain the time constants and the activation energies of four trapping levels. The noise reported here could stem from multilevel trapping in the channel.     

New self-aligned T-gate InGaP/GaAs field-effect transistors grownby LP-MOCVD

This paper reports on self-aligned T-gate InGaP/GaAs FETs using n ⁺/N⁺/δ(P⁺)/n structures. N⁺ -InGaP/δ(P⁺)-InGaP/n-GaAs forms a planar-doped barrier. The inherent ohmic gate of camel-gate FETs together with a highly selective etch between an InGaP and a GaAs layers offers a self-aligned T-shape gate with a reduced effective length. A fabricated device with a reduced gate dimension of 1.5×100 (0.6×100) μm² obtained from 2×100 (1×100) μm² gate metal exhibits an extrinsic transconductance, unity-current gain frequency, and unity-power gain frequency of 78 (80) mS/mm, 9 (19.5), and 28 (30) GHz, respectively     

Comparative investigation of InGaP/GaAs pseudomorphic field-effect transistors with triple doped-channel profiles

In this article, the comparison of DC performance on InGaP/GaAs pseudomorphic field-effect transistors with tripe doped-channel profiles is demonstrated. As compared to the uniform and high-medium-low doped-channel devices, the low-medium-high doped-channel device exhibits the broadest gate voltage swing and the best device linearity because more twodimensional electron gases are formed in the heaviest doped channel to enhance the magnitude of negative threshold voltage. Experimentally, the transconductance within 50% of its maximum value for gate voltage swing is 4.62 V in the low-medium-high doped-channel device, which is greater than 3.58 (3.30) V in the uniform (high-medium-low) doped-channel device.     

Monolithic ultra-broadband transimpedance amplifiers usingAlGaAs/GaAs heterojunction bipolar transistors

Monolithic ultra-broadband transimpedance amplifiers are developed using AlGaAs/GaAs HBTs. To realize good amplifier performances, two factors are mentioned: an affordable HBT fabrication process using the self-aligned method and an optimized circuit design considering large signal operations. The developed HBT fabrication process achieves excellent uniformity in DC characteristics and the effect on amplifier microwave performances, derived from the discrete device uniformity, is estimated. Amplifier circuit configurations are designed by harmonic balance simulation using the extracted large signal device parameters The fabricated amplifier exhibits a DC to 13.4-GHz bandwidth with an 18.1-dB gain. Fairly good uniformity is also achieved for the amplifier microwave performances. An optical receiver module is constructed mounting the developed HBT amplifier and InGaAs p-i-n photodiode chips. The optical receiver module provides a 9.4-GHz bandwidth and an optical receiver sensitivity of -15.7 dBm at 10-Gb/s data rate