Harmonic Enhancement of Terahertz GaN Planar Gunn Oscillators With Multiple Gates

In this paper, we propose a novel design of GaN-based planar Gunn oscillator as terahertz signal source. The oscillator has multiple gates and each gate can be individually biased. By controlling gate bias voltage and distance to the barrier layer, the output oscillating current can be formed in such a way that the higher harmonics are more powerful than the fundamental one. This is because multiple Gunn domains created under the gates in the channel are synchronized. Compared to the conventional single-domain diode, this multi-gate configuration not only increases the frequency and output power but also provides superior harmonic control, leading to higher efficiency and more stable operation at terahertz frequencies. We will review the design details and analysis on domain forming conditions using a physics-based numerical model. The optimal parameters for high power, high DC-RF conversion efficiency and high frequency will be given. Specifically, in dual-gate device, when it works in the dual-domain mode, the second harmonic is enhanced, reaching a frequency of 310.5 GHz with 7.6 mW of power and 11.2% efficiency. The tri-gate device operating in tri-domain mode further enhances the third harmonic to 417.0 GHz, with 9.57 mW of power and 9.23% efficiency. The multi-gate structure allows for more efficient harmonic generation, greater frequency tunability, and better power management, all of which are crucial for advanced terahertz application such as mixing, frequency multiplexing, and signal amplification.