INALAS INGAAS/INP HFET WITH SUPPRESSED IMPACT IONIZATION USING DUAL-GATE CASCODE-DEVICES/

InAlAs/InGaAs dual-gate-HFET's (DGHFET's) and single-gate-HFET's (SGHF ET's) have been fabricated and characterized with special emphasis to reduce impart ionization. For the first time it is shown that in case of the DGHFET, due to the second gate (V-G25 = 0 V), impact ionization can be totally prevented in the channel underneath the rf-driven gate without reduction of rf-relevant parameters as transconductance, outp ut resistance and voltage gain. The electric field and the potential d istribution in the channel is discussed using a nomogram and confirmed by 2-D simulation. According to V-G25 = 0 V, a new cascode design is presented by direct connecting the second gate to the source (ground).