Time-domain Monte Carlo simulations of resonant-circuit operation of GaN Gunn diodes

The time-domain operation of GaAs, InP and GaN vertical n⁺n^-nn⁺ Gunn diodes and GaN planar self-switching diodes (SSDs) is numerically investigated by using the Monte Carlo (MC) technique. To this end, the MC simulation of the intrinsic devices is coupled with the consistent solution of a parallel RLC resonant circuit connected in series. We show that equivalent operating conditions can be achieved by the direct application of a sinusoidal AC voltage superimposed to the DC component. By virtue of the larger saturation velocity of GaN, for a given diode length, oscillation frequencies are higher than for GaAs and InP structures. Current oscillations at frequencies as high as 560 GHz, with a DC to AC conversion efficiency of 0.3%, are predicted at the third harmonic in 1 μm-long GaN diodes. In a 0.5 μm-long GaN SSD, frequencies up to 275 GHz with an efficiency of 0.2% can be achieved, with the advantage of enhanced heat dissipation thanks to the planar geometry.