Monte Carlo study of kink effect in short-channel InAlAs/InGaAs highelectron mobility transistors

Abstract

A semiclassical 2D ensemble Monte Carlo simulator is used to perform a physicalmicroscopic analysis of the kink effect in short-channel InAlAs/InGaAs lattice-matched High Electron Mobility Transistors (HEMTs). Due to the small band gap of InGaAs, these devices are very susceptible to suffer impact ionization processes, with the subsequent hole transport in the channel,both supposedly implicated in the kink effect and easy to be implemented in a Monte Carlosimulation. The results indicate that for high enough VDS , holes, generated by impact ionization,tend to pile up in the channel under the source side of the gate due to the attracting potential caused by the surface charge at the recess and, mostly, by the gate potential. Due to this pile up of positive charge, the potential barrier controlling the current through the channel is lowered, so that the channel is further opened and ID increases, leading to the well known kink effect in the current voltage characteristics. The microscopic understanding of this phenomenon provides valuableinformation to conceive the optimum fabrication process for kink-effect-free HEMTs.

En este trabajo se utiliza un simulador Monte Carlo para analizar a nivel microscópico el origen del efecto kink en transistores HEMT de InAlAs/InGaAs de canal corto. Se encuentra que el fenómeno es debido a huecos, generados por mecanismos de ionización por impacto, que se acumulan en el canal debajo de la puerta del transistor en el lado de la fuente. Tal acumulación reduce la barrera de potencial que controla la corriente que circula por el canal, de modo que ésta aumenta. Se proporcionan indicaciones de diseño para optimizar la fabricación de transistores libres de efecto kink.