Ultra fast Gunn effect at THz frequencies in HEMTs
When the drain-source bias is sufficiently high the emission spectra of HEMTs show peaks at THz frequencies. In this work, we will show the results of Monte Carlo simulations of 80-nm-gate InAlAs/InGaAs HEMTs where ultra-high frequency (in the THz range) Gunn-like oscillations in the gate-drain region of the devices have been observed. Such high frequency implies that the drift velocity of the high field travelling domain approaches 5times105 m/s (a fivefold increase with respect to the steady-state saturation velocity of electrons). This unexpectedly high velocity comes from the presence of extremely fast ballistic electrons in that region, able to go through the high field domain without overcoming intervalley transfer