GaAs IMPATT Research Articles

Large signal and noise properties of heterojunction AlxGa1−xAs/GaAs DDR IMPATTs

Simulation studies are carried out on the large signal and noise properties of heterojunction (HT) AlxGa1−xAs/GaAs double drift region (DDR) IMPATT devices at V-band (60 GHz). The dependence of Al mole fraction on the aforementioned properties of the device has been investigated. A full simulation software package has been indigenously developed for this purpose. The large signal simulation is based on a non-sinusoidal voltage excitation model. Three mole fractions of Al and two complementary HT DDR structures for each mole fraction i.e., six DDR structures are considered in this study. The purpose is to discover the most suitable structure and corresponding mole fraction at which high power, high efficiency and low noise are obtained from the device. The noise spectral density and noise measure of all six HT DDR structures are obtained from a noise model and simulation method. Similar studies are carried out on homojunction (HM) DDR GaAs IMPATTs at 60 GHz to compare their RF properties with those of HT DDR devices. The results show that the HT DDR device based on N-AlxGa1−x As/p-GaAs with 30% mole fraction of Al is the best one so far as large signal power output, DC to RF conversion efficiency and noise level are concerned.

Analysis of SiC IMPATT device in millimeter-wave frequencies

SiC IMPATT devices have an efficiency and power advantage over Si and GaAs IMPATT devices at millimeter-wave frequencies. A lucky drift model describing ionization rates as a function of electric fields at high temperatures has been incorporated into a Read-type large-signal model. The simulation demonstrates that the efficiency (and dc power density) at operating temperature (800 K) for SiC p+n single-drift flat-profile IMPATT structures is 12.4% (6.7 MW/cm2), 15% (4.5 MW/cm2), and 15.8% (3.3 MW/cm2) for frequencies of 200, 100, and 50 GHz, respectively. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 167–168, 1998.

Analysis of SiC IMPATT device in millimeter‐wave frequencies

SiC IMPATT devices have an efficiency and power advantage over Si and GaAs IMPATT devices at millimeter-wave frequencies. A lucky drift model describing ionization rates as a function of electric fields at high temperatures has been incorporated into a Read-type large-signal model. The simulation demonstrates that the efficiency (and dc power density) at operating temperature (800 K) for SiC p+n single-drift flat-profile IMPATT structures is 12.4% (6.7 MW/cm2), 15% (4.5 MW/cm2), and 15.8% (3.3 MW/cm2) for frequencies of 200, 100, and 50 GHz, respectively. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 167–168, 1998.

Large Signal Model of an Optically Controlled GaAs IMPATT Diode

A large signal model of an optically controlled Read-type GaAs IMP ATT diode has been presented. In contrast to other existing theories, we consider the effect of photogenerated carriers in the avalanche zone which significantly affects the device characteristics in the illuminated condition. The model presented here is used to examine the effect of illumination on the output power, efficiency and negative conductance of the device. It has been found that for constant bias current, the output power and efficiency of the device are strong functions of the incident optical power. The model can be used as a basic tool for optimising GaAs IMPATT diodes for optically controlled applications in microwave region.

Computer studies of quasi Read gallium arsenide IMPATT diode: including the effect of space charge

Computer studies have been carried out on the effects of variation of impurity hump parameters of quasi Read high–low (hi–lo) and low–high–low (lo-hi–lo) gallum arsenide IMPATT diodes on their DC and microwave properties. The effect of mobile space charge has been included in the computer analysis. It turns out that the DC properties of the diode are sensitive functions of the width and doping concentration of impurity bumps. The optimum efficiency is found to be respectively 24.5% and 27.9% for hi–lo and lo-hi–lo diodes designed for 18 GHz frequency. The small signal admittance calculations show that a lo-hi–lo structure provides higher negative conductance and better quality factor compared with a hi–lo structure of GaAs Impatt diode.

A resonant-cap power combiner for two-terminal millimeter-wave devices

A power combiner for three active two-terminal devices located under a common resonant cap is presented. An equivalent circuit with lumped elements describing the coupling between the devices is derived from a numerical finite-element simulation of the resonator. The applied monolithically integrated mounting technique for the active devices minimizes parasitic elements and gains high reproducibility and symmetry. Experimental results with GaAs IMPATT diodes on diamond heatsink of up to 500 mW at 91 GHz with a dc to RF conversion efficiency of 9.0% and excellent combining efficiency demonstrate the capability for power generation in the mm-wave region.

Proposed GaAs IMPATT device structure for D-band applications

A GaAs double drift IMPATT device structure for applications in D-band is proposed which exhibits high efficiencies at relatively high impedance levels. Computer simulations using a full hydrodynamic transport model with two additional energy balance equations for accurate modelling of impact ionisation show that under realistic thermal considerations, output powers up to 400 mW should be obtainable around 150 GHz. >

New mounting technique for two-terminal millimetre-wave devices

A new mounting technique for two-terminal devices is presented which minimises parasitic elements and improves thermal heat resistance. Monolithic fabrication of the structure leads to high reproducibility. First experimental results for power generation at W-band frequencies with GaAs Impatt diodes are reported. >

Active two-terminal devices as local oscillators for low-noise receiver systems at submillimeter wave frequencies

The power capabilities of three different two-terminal devices, GaAs IMPATT diodes, InP Gunn devices and GaAs TUNNETT diodes are evaluated. Two different selective etching technologies have been employed to fabricate devices on either a diamond heat sink or an integral heat sink. The reported RF power levels in fundamental mode are 20 mW at 120 GHz and 15 mW at 135 GHz for D-band GaAs IMPATT diodes, 21 mW at 120 GHz, 17 mW at 133 GHz and 8 mW at 155 GHz for D-band InP Gunn devices and up to 35 mW around 103 GHz for W-band GaAs TUNNETT diodes. Typical de to RF conversion efficiencies range from 0.9% up to over 4.0%. In second harmonic mode power levels of 0.25 mW at 223 GHz were measured from TUNNETT diodes and 0.4 mW at 220 GHz from a Gunn device.

Studies on the high-frequency properties of ?111?, ?110? and ?100? oriented GaAs IMPATT diodes

High-frequency analysis has been carried out to predict the rf performance of 〈111〉, 〈110〉 and 〈100〉 oriented p+nn+, n+pp+ (single drift region) and n+npp+ (double drift region) GaAs IMPATT diodes for opertion at 35 and 60 GHz. The microwave performance is observed to be highly sensitive to crystal orientation in case of p+nn+ and n+npp+ diodes whereas orientation of the substrate has negligible effect on n+pp+ avalanche diodes. The calculation shows that 〈111〉 oriented GaAs IMPATT diode would provide the largest magnitude of negative resistance and negative conductance for both SDR p+nn+ and DDR n+npp+ diodes which indicates that high microwave power with high conversion efficiency can be realised from these 〈111〉 oriented GaAs devices. This result can be explained from the experimental data of electron and hole ionization rates for different orientations in GaAs.

Low noise, high efficiency GaAs IMPATT diodes at 30 GHz

Low noise, very high efficiency IMPATT diodes provide an attractive alternative to Gunn diodes for many millimetre-wave applications. In the Letter, GaAs Hi–Lo single-drift IMPATT diodes are demonstrated. The diodes are fabricated using molecular beam epitaxy and (at ~30 GHz) exhibit exceptional efficiencies (>20%), very low FM noise (–88 dBc/Hz at 100 kHz off-carrier) and simultaneous CW power levels in excess of 300 mW.

GaAs single-drift flat-profile IMPATT diodes for CW operation at D band

Single-drift flat-profile GaAs IMPATT diodes were designed for CW operation in the 140GHz range. The diodes were fabricated from MBE grown material, mounted on diamond heatsinks and tested in a radial line full height waveguide cavity. An RF output power of 15 mW with a corresponding DC to RF conversion efficiency of 1.5 % was obtained at 135.3 GHz

Temperature dependence of electron saturation velocity in GaAs

Electron saturation velocity is determined from the space charge resistance R/sub c/ and microwave impedance Z/sub d/ of GaAs IMPATT diodes under linear conditions. Comparison between experimental measurement and theory is used in a large frequency bandwidth (2-18 GHz) at different temperatures (T<or=500 K). The results obtained are in good agreement with those of other authors.

Selective etching technology for 94 GHz GaAs IMPATT diodes on diamond heat sinks : Heribert Eisele. Solid-St. Elect.32(3), 253 (1989)

Selective etching technology for 94 GHz GaAs IMPATT diodes on diamond heat sinks : Heribert Eisele. Solid-St. Elect.32(3), 253 (1989)

High frequency characterisation of double drift region InP and GaAs diodes

Computer studies have been made on the high frequency characteristics of symmetrically doped flat profile double drift region (DDR) InP and GaAs impatts in the mm-wave (60–100 GHz) frequency band. The spatial distribution of high frequency negative resistance and reactance in the depletion layer of DDR devices and their admittance properties have been investigated. The results indicate that DDR InP impatts should have higher drift zone voltage drop, higher negative resistance and higher negative conductance compared to their GaAs counterparts designed for the same range of mm-wave frequencies. Furthermore, the negative resistance peak is larger in magnitude for InP impatts compared to that for GaAs impatts. It is thus observed that DDR InP impatts should be superior to their GaAs counterparts as regards mm-wave power generation with high conversion efficiency.

Selective etching technology for 94 GHz GaAs IMPATT diodes on diamond heat sinks

A selective etching technology has been established for 94 GHz GaAs IMPATT diodes operating on diamond heat sinks. Using this technology diodes were realized delivering an output power of 270 mW. The corresponding efficiency was 5.7% at an oscillation frequency of 95 GHz.

Millimeter-wave monolithic GaAs IMPATT VCO

A monolithic voltage-controlled oscillator (VCO) has been constructed using a GaAs double-drift Read IMPATT as the active element and a similar diode biased below breakdown as the varactor. The chip produced 120-mW peak power over an electronically controlled tuning range between 47 and 48 GHz. A computer analysis based on characterized circuit parameters has been used to predict the performance of the chip.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monolithic millimeter-wave IMPATT oscillator and active antenna

A single-chip millimeter-wave transmitter module in which GaAs IMPATT diodes are monolithically integrated with a microstrip resonator and a loop antenna is discussed. Devices operating at 43.3 GHz produce 27-mW CW output power with 7.2% conversion efficiency. Radiation patterns of linear arrays of such radiating elements were determined as a function of interelement spacing and number of elements. The oscillator chip was also directly coupled to and power combined in waveguides, producing an inexpensive millimeter-wave source. >

Anomalous temperature variation of the thermal resistivity of GaAs IMPATT diodes

The thermal resistivity of GaAs IMPATT diodes was measured from 100-325 degrees C and showed an unexpected 10% decrease, in contrast with the behavior of GaAs MESFET devices, whose resistivity increases as much as 30% over the same temperature range. The most likely explanation of this unusual effect is the dominance of charged impurity scattering in a degenerately doped GaAs contact layer. This may be expected to occur in other devices where heat flow crosses highly doped regions. >

Monolithic 60 GHz GaAs IMPATT oscillators

A monolithic circuit design developed for GaAs IMPATT diodes to enable them to operate under CW conditions at V-band frequencies is discussed. All active and passive circuit components were fabricated on the top surface of the GaAs substrate. Good heat dissipation was achieved by distributing the device active area over a large surface area while maintaining a lumped mode of operation. More than 100-mW CW output power was obtained in the 58-65-GHz frequency range, with up to 14.5% conversion efficiency. In an alternative design, varactor diodes were integrated with the IMPATT circuits to produce the first monolithic voltage-controlled oscillators (VCOs) operating under CW conditions. A tuning bandwidth greater than 3.5 GHz was obtained at a center frequency of 70 GHz, with maximum CW output power of 40 mW. >