Ridha Kamoua

Submillimeter-wave InP Gunn devices

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.

Monte Carlo-based harmonic-balance technique for the simulation of high-frequency TED oscillators

A harmonic-balance technique for the analysis of high-frequency transferred electron device (TED) oscillators is developed. The behavior of the nonlinear TED is not obtained from a quasi-static equivalent circuit; rather, a physical transport model is used to determine its response in the time domain. This model is based on the ensemble Monte Carlo technique coupled to a heat-flow equation, which accounts for thermal effects on the device operation. It is found that the standard splitting method for updating the unknown voltage across the diode fails to converge to a steady-state solution at the fundamental frequency. A modified version is proposed, which updates the voltage at the fundamental and higher harmonics differently. This method exhibits much better convergence behavior. Simulation results obtained with the complete model are in very good agreement with experimental data from InP TED oscillators operating at 131.7 and 151 GHz in the fundamental mode and at 188 GHz in the second-harmonic mode.

High-performance oscillators and power combiners with InP Gunn devices at 260-330 GHz

InP Gunn devices with graded doping profiles were evaluated for second-harmonic power extraction above 260 GHz. The best devices generated radio frequency(RF) output power levels of 3.9 mW at 275 GHz, 4.8 mW at 282 GHz, 3.7 mW at 297 GHz, 1.6 mW at 329 GHz, and 0.7 mW at 333 GHz with corresponding dc-to-RF conversion efficiencies of 0.24%, 0.31%, 0.32%, 0.19%, and 0.07%. The highest observed second-harmonic frequency was 345 GHz. Two devices each in an in-line power combining circuit generated 6.1 mW at 285 GHz and 2.7 mW at 316 GHz with combining efficiencies of more than 65%.

An Upper Bound for the Bisection Width of a Diagonal Mesh

Recently, it was correctly pointed out by Jha that there is an error in our earlier paper on diagonal mesh networks. In response to Jhas critique, we now provide an upper bound on the bisection width of a diagonal mesh. The proof is a constructive one and an algorithm is provided to divide the network into two equal halves (plus/minus one node)

Theoretical and experimental comparison of optimized doping profiles for high-performance InP Gunn devices at 220-500 GHz

Different types of doping profiles are investigated theoretically and experimentally for their potential of improving the performance of InP Gunn devices at J-band (220-325 GHz) frequencies and above. As initial experimental results, devices with an optimized graded doping profile generated output power levels approximately twice the previous state-of-the-art values at 280-300 GHz. Simulations identified a fiat doping profile with a notch at the cathode as even more promising. For example, an RF output power of 50 mW at 240 GHz is predicted for this profile compared to 42 mW at 240 GHz from an optimized graded doping profile.

Development of an appropriate model for the design of D-band InP Gunn devices

The potential of InP Gunn devices as power sources in the fundamental mode at D-band frequencies (110 GHz-170 GHz) is investigated. A self-consistent ensemble Monte Carte model has been developed to design and identify suitable structures for operation in this frequency range. Using this model with typical InP material parameters found in the literature, it is shown to give results inconsistent with experiment. Based on experimental results from a 1.7 /spl mu/m long Gunn structure, more realistic material parameters were estimated. The resulting model is then used to design various structures with active regions in the 1 /spl mu/m range. In particular, two structures, one with a flat doping profile and the other with a linearly graded doping profile, were fabricated and tested. State-of-the-art performance from these structures operating in the fundamental mode was obtained at frequencies ranging from 108.3 GHz to 155 GHz. The flat structure yielded optimum results at 108.3 GHz with a power level of 33 mW while the graded structure gave 20 mW at 120 GHz, 17 mW at 133 GHz, 10 mW at 136 GHz, and 8 mW at 155 GHz. These results are compared with the model predictions.<<ETX>>