Potential of GaN Gunn Devices for High Power Generation Above 200 GHz
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Potential of GaN Gunn Devices for High Power Generation Above 200 GHz Ridha Kamoua, Yiming Zhu, Yunji Corcoran1 Dept. of Electrical and Computer Engineering, SUNY at Stony Brook, Stony Brook, NY 11794-2350, U.S.A. 1 RSM Sensitron Deer Park, NY 11729-4681, U.S.A. ABSTRACT This paper investigates the potential of Gallium Nitride (GaN) Gunn diodes for generating high power radiation at millimeter and sub-millimeter wave frequencies. Simulations were carried out based on an ensemble Monte Carlo computer model. This model accounts for thermal effects, series resistance, and device circuit interaction through the harmonic balance technique. The accuracy of the model has been validated in the case of InP Gunn devices at frequencies above 100 GHz[1]. Initially uniform and linearly graded doping profiles in the active region were considered. It is found that, similar to devices based on InP, the graded profile resulted in a much improved performance in terms of power, efficiency, and operating temperature. In particular, a GaN Gunn structure consisting of a 1 µm thick active region with a graded doping profile increasing from 6 × 1015 cm-3 at the cathode terminal to 4.6 × 1016 cm-3 at the anode terminal yielded promising results. The DC bias voltage was estimated from the calculated velocity-electric field data to be about 25 V. With this bias, it was found that oscillations in the fundamental mode could be obtained over the frequency range from 220 GHz to 330 GHz subject to a load resistance of 1 Ohm and a maximum operating temperature of 800 K. The maximum output power was 30 mW at 290 GHz with a corresponding conversion efficiency of 0.25 %. Considerable improvement was obtained from a device with a heterojunction at the cathode. For a 1 µm device, an optimum power level close to150 mW was predicted at 215 GHz with an efficiency of 2 %. This estimated power level is about an order of magnitude higher than what can be achieved from InP Gunn oscillators at the same frequency. INTRODUCTION Many applications in the millimeter and submillimeter wave regions of the electromagnetic spectrum require compact solid-state local oscillators that provide low noise and adequate power levels. Oscillators based on GaAs and InP Gunn devices have been widely used to serve this purpose at frequencies up to 140 GHz. These devices have proved to be reliable with excellent amplitude and phase noise characteristics. For high frequency operation, the principle limiting factor is the semiconductor material itself as the Gunn effect is directly realted to the bandstructure and the material properties of the semiconductor. Gunn devices based on GaAs are limited to W-band (70 – 110 GHz) whereas InP devices have been shown to generate considerable power levels up to 140 GHz. Table 1 compares GaAs, InP, and zincblende GaN material and band structure parameters of importance to the Gunn effect.
T2.6.1
Bandgap energy (eV) Energy separation (eV) Effective mass (
m* m0
)
Γ−L Γ− X Γ L
X Threshold electric field (kV/cm) Thermal conductivity (W/cm.K)
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