Terahertz Gunn-like oscillations in InGaAs/InAlAs planar diodes

A microscopic analysis of self-generated terahertz current oscillations that take place in planar InAlAs/InGaAs slot diodes operating under dc bias is presented. An ensemble Monte Carlo simulation is used for the calculations. The onset of the oscillations is thresholdlike, for drain-source voltages surpassing 0.6 V. The Gunn-like mechanisms and the modulation of the injection of electrons into the recess-to-drain region, which alternatively takes place in the Γ or L valley, are found at the origin of the phenomenon. Terahertz frequencies are reached because of the presence of ultrafast Γ electrons in the region of interest. Extremely high velocities are achieved by (i) the effect of the recess, which focuses the electric field and launches very fast electrons into the drain region, and (ii) the influence of degeneracy, which significantly reduces the rate of scattering mechanisms and enhances the electron mobility in the channel.