Monte Carlo study of impact ionization and hole transport in InAs HEMTs with isolated gate

We present a physical analysis of the kink effect in InAs/AlSb High Electron Mobility Transistors (HEMTs) performed by means of a semiclassical 2D ensemble Monte Carlo simulator. InAs-channel HEMTs are very susceptible to suffer from impact ionization phenomena due to the small bandgap of InAs. These processes, jointly with the associated hole transport, are at the origin of the kink effect. When the drain-to-source voltage is high enough for the onset of impact ionization, generated holes tend to accumulate at the gate-drain side of the buffer because of the valence-band energy barrier present between the buffer and the channel. Due to this pile up of positive charge the channel is further opened and the drain current increases, leading to the kink in the I-V characteristics.