Collector-up AlGaAs/GaAs HBTs using oxidized AlAs

Summary form only given. Collector-up HBTs offer a means to reduce base-collector capacitance relative to their emitter-up counterparts, and thus to improve microwave power gain and digital switching speeds. Collector-up structures afford the device designer extra latitude is choosing collector doping and are amenable to graded base designs as the base contact is now made to GaAs rather than AlGaAs. Current methods of fabricating collector-up AlGaAs/GaAs heterojunction bipolar transistors normally use either ion implantation or a three stage growth process. Here we describe a novel method for fabricating collector-up AlGaAs/GaAs HBTs. An AlAs layer is inserted into the emitter layer and is oxidized in water vapor at 450/spl deg/C. The resulting AlAs-oxide serves as a current confining layer that constricts collector current flow to the intrinsic portion of the device. Compared to conventional methods, the process of converting AlAs into an insulator in the emitter requires only one growth, and does not suffer from implant damage in the base. DC devices with typical current gains of 50 are observed.