Simulation of impact ionization breakdown in MESFETS using Monte Carlo methods

Abstract

We have investigated impact ionization in a small 1.2 µm MESFET by means of Monte Carlo simulation. Whilst ionization in devices operating near pinch-off was found to occur in accordance with the nominal gate-drain electric field, it was found that at lower gate reverse bias the device was vulnerable to oscillating electric fields associated with the formation of accumulation layers. These fields caused significant impact ionization to occur at relatively low nominal gate-drain potentials. Indeed the newly formed holes could have a positive feedback effect on the potential causing the oscillations to increase and the device to eventually break down. Under certain circumstances, the accumulation layer oscillations were stable and the device oscillated with a frequency of ≈125 GHz, though as the displacement current was out of phase with the carrier current, the total current was found to have little more than a ripple on it.

Current instability in power HEMTs

“…The possible role of accumulation layers in the breakdown of FETs was also investigated theoretically in [5,6]. There has, however, been relatively little good corroborating experimental evidence for the existence of such Gunn instabilities with that presented in [5] and [6] being very indirect.…”

Monte Carlo simulation of THz frequency range Gunn effect in InP MOSFET at impact ionization conditions

“…The breakdown potential of the device decrease with increasing gate voltage and is in agreement with ref. [1]. The stationary 200 GHz Gunn drain current oscillations arise at sufficiently high (of about 3 V) forward gate bias, where the drain bias U d is 1.8 V (see Fig.2).…”

“…The Gunn effect at impact ionization conditions in GaAs MESFET is simulated by Monte Carlo particle (MCP) technique [1], where 125 GHz drain current oscillations at 400 nm gate length were predicted. Also 50 GHz drain current oscillations at impact ionization conditions in AlGaAs/InGaAs HEMTs are shown by MCP technique [2].…”

Monte Carlo simulation of THz frequency Gunn effect in GaAs MOSFET with excess of electrons in channel at impact ionization conditions

“…The Gunn effect at impact ionization conditions in GaAs MESFET is simulated by Monte Carlo particle (MCP) technique [1]. The 125 GHz drain current oscillations are demonstrated.…”