Large-Signal Analysis of Terahertz Generation in Submicrometer GaN Diodes

The conditions for microwave power generation in a submicrometer GaN diode, with a relatively lightly doped active channel, coupled to an external resonant circuit are investigated. Applying a high-field electron transport model based on the local quasi-static approximation, we show that oscillations in group III-nitride diodes can be supported in the terahertz-frequency range near the limited space-charge accumulation regime. The shape of the diode voltage and electronic current waveforms are examined in terms of the circuit parameters and operating frequencies over the bandwidth of active generation. Based on a Fourier series analysis of the diode voltage and current, the generated power and dc-to-RF conversion efficiency at the fundamental and the second or higher order harmonic frequencies are estimated. The calculation results clearly indicate that submicrometer GaN diodes (channel doping of 1 × 10¹⁷ cm^-3) can achieve large output powers (> 1 W) in the absence of Gunn domain formation, over a wide range of frequencies, near 0.5 THz.