High-f/sub max/ Collector-up AIGaAs/GaAs Heterojunction Bipolar Transistors with a Heavily Carbon-Doped Base Fabricated by Oxygen-ion implantation

Summary form only given. The authors demonstrate the superiority of the first collector-up (C-up) HBTs (heterojunction bipolar transistors) with a heavily carbon (C)-doped base layer fabricated by oxygen-ion (O/sup +/) implantation to define the intrinsic emitter/base junction and zinc (Zn) diffusion to reduce base contact resistance. A maximum oscillation frequency f/sub max/ of 126 GHz was obtained; this exceeds that of the C-up HBT fabricated by proton (H/sup +/) implantation. A key process in fabrication of C-up structures is the formation of an external emitter/base junction to effectively suppress the parasitic base leakage current. The formation of a high-resistivity AlGaAs 'barrier' between the external base and emitter buffer layers is effective for this purpose. For microwave transistors with collector dimension of 2 mu m*10 mu m, a cutoff frequency f/sub T/ of 56 GHz and f/sub max/ of 125 GHz were attained. >