Characterization of degradation mechanisins in GaAs/AlGaas heterojunction bipolar transistors

The devices are fabricated using similar structures grown by MOMBE', with Sn and C as dopants. The growth sequence includes a 62 nm GaAs base ( p = 7 ~ 1 0 ' ~ c m ~ ) , a 7 nm GaAs undoped spacer, and a 80 nm Alo.25 Gao.75 As emitter (n= 6x lo'* cm). The main fabrication technology uses a self-aligned process based on dry etching with AuGe metallization and ion-implant isolation, This process, which we refer to as the "implant process", is similar to that described in ref. 2, but with a tri-layer lift-off ste for the base metallization and higher implant doses. The implant includes total doses of 1 . 8 ~ 1OI6 cmH+ and 1014cm-2 F+ and is followed by annealing at 53OOC. A second process (the "W process") replaces the AuGe metallization with WSi, and the ion-implantation with mesa isolation and a semiplanarized geometry.