The GaN material parameters relevant to the negative diAerential resistance (NDR) devices are discussed, and their physical models based on the theoretical predictions and experimental device characteristics are introduced. Gunn diode design criteria were applied to design the GaN NDR diodes. A higher electrical strength of the GaN allowed operation with higher doping (10 17 cm ˇ3 ) and at a higher bias (90 V for a 3 lm thick diode). The transient hydrodynamic simulations were used to carry out the harmonic power analysis of the GaN NDR diode oscillators in order to evaluate their large-signal microwave characteristics. The GaAs Gunn diode oscillators were also simulated for a comparison and verification purposes. The dependence of the oscillation frequency and output power on the GaN NDR diode design and operating conditions are reported. It was found that, due to the higher electron velocities and reduced time constants, GaN NDR diodes oAered twice the frequency capability of the GaAs Gunn diodes (87 GHz vs. 40 GHz), while their output power density was 2 10 5 W/cm 2 compared with10 3 W/cm 2 for the GaAs devices. The reported improvements in the microwave performance are supported by the high value of the GaN Pf 2 Z figure of merit, which is 50‐100 times higher than the GaAs, indicating a strong potential of the GaN for the microwave signal generation. ” 2000 Elsevier Science Ltd. All rights reserved.

Large-signal microwave performance of GaN-based NDR diode oscillators

Recent advances in design and technology significantly improved the performance of low-noise InP Gunn devices in oscillators first at D-band (110-170 GHz) and then at W-band (75-110 GHz) frequencies. More importantly, they next resulted in orders of magnitude higher RF output power levels above D-band and operation in a second-harmonic mode up to at least 325 GHz. Examples of the state-of-the-art performance are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3.5 mW at 300 GHz, and more than 2 mW at 315 GHz. The dc power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Two different types of doping profiles, a graded profile and one with a doping notch at the cathode, are prime candidates for operation at submillimeter-wave frequencies. Generation of significant RF power levels from InP Gunn devices with these optimized doping profiles is predicted up to at least 500 GHz and the performance predictions for the two different types of doping profiles are compared.

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Submillimeter-wave InP Gunn devices

Design and optimization of Schottky varactor diode frequency multipliers for millimeter and submillimeter wavelengths are generally performed using harmonic balance techniques together with equivalent-circuit models. Using this approach, it is difficult to design and optimize the device and multiplier circuit simultaneously. The work presented in this paper avoids the need of equivalent circuits by integrating a numerical simulator for Schottky diodes into a circuit simulator. The good agreement between the calculated and published experimental data for the output power and conversion efficiency originates from the accurate physical model. The limiting effects of multiplier performance such as breakdown, forward conduction, or saturation velocity are discussed in view of the optimum circuit conditions for multiplier operation including bias point, input power, and loads at different harmonics. It is shown that the onset of forward or reverse current flow is responsible for the limitation in the conversion efficiency.

Modeling and design aspects of millimeter-wave and submillimeter-wave Schottky diode varactor frequency multipliers

Mass transport and kinetic limitations in MOCVD selective-area growth

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.

https://publications.lib.chalmers.se/records/fulltext/local_2106.pdf

Heterostructure-barrier-varactor design

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.

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

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 Poisson's 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.

125–145 GHz stable depletion layer transferred electron oscillators

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. >

http://ieeexplore.ieee.org/iel4/75/7900/00336230.pdf

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

Nonuniform and enhanced growth rates due to gas-phase diffusion are calculated for vapor phase selective epitaxy. By solving Laplace's equation above a partially masked growth substrate, the effects of gas phase diffusion on vapor phase selective epitaxy are considered. Surface features having a single dielectric masking stripe or series of periodically spaced masking stripes are analyzed. Closed form expressions are given for reactant concentrations and enhanced growth rates away from the edge of a large single masking stripe, and similar calculations are made for the case of repetitive masking stripes. These calculations compare favorably with low pressure organometallic vapor phase selective epitaxy of GaAs and InAs on SiO 2 masked GaAs substrates.

A simplified model describing enhanced growth rates during vapor phase selective epitaxy

Accurate and efficient simulations of the large-signal time-dependent characteristics of second-harmonic transferred electron oscillators (TEO's) and heterostructure barrier varactor (HBV) frequency triplers have been obtained. This is accomplished by using a novel and efficient harmonic-balance circuit analysis technique which facilitates the integration of physics-based hydrodynamic device simulators. The integrated hydrodynamic device/harmonic-balance circuit simulators allow TEO and HBV circuits to be co-designed from both a device and a circuit point of view. Comparisons have been made with published experimental data for both TEO's and HBV's. For TEO's, excellent correlation has been obtained at 140 GHz and 188 GHz in second-harmonic operation. Excellent correlation has also been obtained for HBV frequency triplers operating near 200 GHz. For HBV's, both a lumped quasi-static equivalent circuit model and the hydrodynamic device simulator have been linked to the harmonic-balance circuit simulator. This comparison illustrates the importance of representing active devices with physics-based numerical device models rather than analytical device models. >

M.F. Zybura

Papers

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

125–145 GHz stable depletion layer transferred electron oscillators

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

A simplified model describing enhanced growth rates during vapor phase selective epitaxy

Simulation of 100-300 GHz solid-state harmonic sources