Velocity overshoot effects and transit times in III-V nitride HFETs : a Monte Carlo study

Abstract

Monte Carlo simulation of AlGaN/GaN HEMTs were carried out and compared with GaAs based devices. The following outcomes of our simulations are noteworthy: i) partially due to the relatively heavy electron effective mass in GaN, the velocities of the electrons are mostly below the steady state values through most of the channel; ii) unlike what is observed in GaAs based short channel devices, there is no pronounced overshoot effect, even at high drain source biases, due to increased scattering; iii) our simulations show that the suppression of overshoot is directly related to the length of the high field region. This length is quite small for usual bias conditions. We suggest that a non-uniform composition of the barrier region could conceivably help in spreading out the high field region, which is present at the drain end of the device. Other results of the Monte Carlo simulation include transconductance, noise information and unity current gain frequency.