InAlAs/InGaAs/InP HFET with suppressed impact ionization using dual-gate cascode-devices

InAlAs/InGaAs dual-gate-HFETs (DGHFETs) and single-gate-HFETs (SGHFETs) have been fabricated and characterized with special emphasis on reducing the impact ionization. For the first time it is shown that in the case of the DGHFET, due to the second gate (V/sub G2S/=0 V), impact ionization can be totally prevented in the channel underneath the RF-driven gate without reduction of the RF-relevant parameters such as transconductance, output resistance and voltage gain. The electric field and the potential distribution in the channel are discussed using a nomogram and confirmed by 2-D simulation. According to V/sub G2S/=0 V, a new cascode design is presented by directly connecting the second gate to the source (ground).