Stephen H. Jones

Effects of self-heating on planar heterostructure barrier varactor diodes

The conversion efficiency for planar Al/sub 0.7/GaAs-GaAs heterostructure barrier varactor triplers is shown to be reduced from a theoretical efficiency of 10% to 3% due to self-heating. The reduction is in accordance with measurements on planar Al/sub 0.7/GaAs-GaAs heterostructure barrier varactor (HBV) triplers to 261 GHz at room temperature and with low temperature tripler measurements to 255 GHz. The delivered maximum output power at 261 GHz is 2.0 mW. Future HBV designs should carefully consider and reduce the device thermal resistance and parasitic series resistance. Optimization of the RF circuit for a 10 /spl mu/m diameter device yielded a delivered output power of 3.6 mW (2.5% conversion efficiency) at 234 GHz.

Patterned substrate epitaxy surface shapes

Abstract This article describes a comprehensive technique to determine the shapes of GaAs epitaxial layers grown by organometallic chemical vapor deposition (OMCVD) on patterned substrates. A simple technique called the Borgstrom construction, which can predict epitaxial shapes, is reviewed. However, the assumptions in this model limit its applications and the Wulff construction is needed. The Wulff construction can predict edge shapes for constrained and unconstrained (such as at the edge of a mask) epitaxial growth. This technique is valid for any geometric situation assuming the growth rate versus orientation (growth rate polar diagram) is known. A semi-empirical growth rate polar diagram is given for GaAs at 750°C and atmospheric pressure OMCVD. The predictions made by the Wulff construction compare favorably with experimental results.

Heterostructure-barrier-varactor design

In this paper, we propose a simple set of accurate frequency-domain design equations for calculation of optimum embedding impedances, optimum input power, bandwidth, and conversion efficiency of heterostructure-barrier-varactor (HBV) frequency triplers. A set of modeling equations for harmonic balance simulations of HBV multipliers are also given. A 141-GHz quasi-optical HBV tripler was designed using the method and experimental results show good agreement with the predicted results.

Planar multibarrier 80/240-GHz heterostructure barrier varactor triplers

Prototype planar four barrier GaAs/Al/sub 0.7/Ga/sub 0.3/As heterostructure barrier varactors (HBVs) for frequency tripling from 80 to 240 GHz have been fabricated using a process in which the device surface channel is etched prior to the formation of the contact pad-to-anode air-bridge finger. Formation of the device air-bridge finger after etching the surface channel is facilitated by a trench planarization technique and yields a device with minimal parasitic capacitances. Planar four-barrier HBV triplers with nominal 10-/spl mu/m diameter anodes have been tested in a crossed-waveguide tripler block; as much as 2 mW of power has been generated at 252 GHz with a flange to-flange tripling efficiency of 25%. These devices are the first planar or multibarrier HBV triplers reported and their output powers are nearly double that of previous whisker-contacted single-barrier HBVs.

GAAS DEVICES AND CIRCUITS FOR TERAHERTZ APPLICATIONS

Abstract GaAs diodes are used as mixer and multiplier elements throughout the terahertz frequency range. This is primarily because the technology is well-understood, convenient to use and supplies adequate performance for most applications. GaAs Schottky diodes are the mixer element of choice for terahertz applications where the added expense of cryogenic superconductive (SIS) or hot electron bolometric (HEB) mixers is not warranted. Furthermore, GaAs (and InP) multiplier diodes, used in conjunction with millimeter wave oscillators, are presently the best available technology for generating terahertz power from solid-state sources. In this paper, we will first review the status of terahertz diode technology with emphasis on the recent results which define the cutting edge of diode performance. We will then discuss the improvements that are needed to ensure that this technology not only meets the expanding needs of scientific researchers, but also is extended to future military and commercial applications.

Pseudomorphic GaAs/InGaAs single quantum wells by atmospheric pressure organometallic chemical vapor deposition

High‐quality pseudomorphic GaAs/In0.12Ga0.88As single quantum wells (QW’s) were prepared by atmospheric‐pressure organometallic chemical vapor deposition. Photoluminesence spectra measured at 2.5 and 78 K exhibit intense, sharp peaks [full width at half‐maximum (FWHM)=2.6 meV for a 17‐A well at 78 K] from the quantized energy transitions of the QW’s. Peak positions agree well with a square well calculation that includes the strain‐induced band‐gap shift in the In0.12Ga0.88As. Quite unlike previous work with QW’s in which the FWHM was found to exponentially increase with decreasing well width, we observed a narrowing of the QW signals as the well width went below ∼30 A. In larger well samples (300 A), the onset of surface crosshatch patterns was observed, which is expected from critical thickness theory.

Monte Carlo harmonic-balance and drift-diffusion harmonic-balance analyses of 100-600 GHz Schottky barrier varactor frequency multipliers

To date, high frequency multipliers have been designed and analyzed using harmonic-balance codes incorporating equivalent circuit models for the diodes. These codes, however, are unable to accurately predict circuit performance at frequencies above 100 GHz and do not allow a means for studying the physics of electron transport. In order to analyze these high frequency Schottky doublers, a novel harmonic-balance technique has been integrated into a drift-diffusion numerical simulator and, for the first time, a Monte Carlo numerical device simulator. The unification of the numerical device simulator with the harmonic-balance algorithm allows for the self-consistent study of electron transport phenomena as well as the study of device performance in a given circuit. These combined simulators are tested against experimental data and an equivalent circuit model harmonic-balance approach, and yield superior accuracy with respect to the experimental data.

Heterostructure barrier varactor simulation using an integrated hydrodynamic device/harmonic-balance circuit analysis technique

Accurate and efficient simulations of the large-signal time-dependent behaviour of GaAs-AlGaAs Heterostructure Barrier Varactor (REV) frequency tripler circuits have been obtained. This is accomplished by combining a novel harmonic-balance circuit analysis technique with a physics-based hydrodynamic device simulator. The integrated HBV hydrodynamic device/harmonic-balance circuit simulator allows HBV multiplier circuits to be co-designed from both a device and a circuit point of view. Comparisons are made with the experimental results of Choudhury et al. (see IEEE Trans. Microwave Theory Tech., vol. 41, no. 4, p. 595-9, 1993) for GaAs-AlGaAs HBV frequency triplers operating near 200 GHz. These comparisons illustrate the importance of representing active devices with physics-based numerical device models rather than analytical device models based on lumped quasi-static equivalent circuits.<<ETX>>

125–145 GHz stable depletion layer transferred electron oscillators

Abstract In this paper, the improved performance of transferred electron devices utilizing current limiting contacts is clearly illuminated. With the appropriate cathode contact, these devices operate in a novel stable depletion layer mode characterized by an oscillating stable depletion layer rather than an unstable propagating accumulation layer or dipole. A small-signal model is offered to explain the stable small-signal resistance of the device over a broad frequency range. Large-signal analysis is completed using a hydrodynamic device simulator employing the temperature-dependent drift-diffusion equation and Poissons equation combined with a novel harmonic-balance circuit analysis technique. Analysis of the electric fields, electron concentration, and device temperature is included for steady-state large-signal operation. Embedding impedances are extracted for a D-band cavity, and performance comparisons are made with experimental data for second-harmonic operation from 125 to 145 GHz with excellent correlation. High reliability operation and as much as 65 mW of output power at 138 GHz is achievable.

Efficient computer aided design of GaAs and InP millimeter wave transferred electron devices including detailed thermal analysis

Abstract An accurate calculation of the large-signal a.c. behavior with detailed thermal considerations is presented for GaAs and InP transferred electron devices. This is accomplished by sequentially solving the temperature dependent drift and diffusion equations along with a novel heat flow analysis to update the temperature profile in the device. The drift and diffusion equations employ both field and temperature dependent mobility and diffusivity derived from Monte Carlo simulations, and the thermal analysis includes all regions of the device. Simulation results are compared to experimental devices with good agreement. The relationship between the graded active layer doping profiles, device area and device length, with the device temperature, output power and device admittance is clearly illuminated by the temperature dependent large-signal a.c. simulator. For the devices simulated, the complex device admittances are calculated over the range of stable operation and at the maximum power point.