Monte Carlo Study of Gunn Oscillations in Geometrically Shaped Planar Gunn Diodes Based on Doped GaN: Influence of Geometry, Intervalley Energy, and Temperature

An investigation into self-switching diodes based on highly doped GaN is conducted under direct current (dc) bias conditions. Different device geometries are explored under various lattice temperatures and polarization scenarios. Also, the impact of adopting an intervalley energy <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{{1}-{2}} =0.9$ </tex-math></inline-formula> eV for this material is examined and compared with results obtained with the traditionally accepted value of 2.2 eV. For a rectangular channel configuration, simulations predict oscillation frequencies in excess of 200 GHz, much above the expected transit-time value, due to the fact that the Gunn domains are formed near the anode side of the channel. Conversely, structures with a V-shaped geometry are able to start the formation of the Gunn domain inside the channel, thus generating oscillations at much lower frequencies (tens of gigahertz). The key result is that the lower <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{{1}-{2}}$ </tex-math></inline-formula> leads to smaller threshold voltage values (and also slightly smaller oscillation frequencies), particularly in diodes with short channels.