253-GHz f/sub max/ AlGaAs/GaAs HBT with Ni/Ti/Pt/Ti/Pt-contact and L-shaped base electrode

We have developed a 253 GHz f/sub max/ AlGaAs/GaAs HBT with a C-doped (4/spl times/10/sup 19/ cm/sup -3/) base layer, using two techniques to decrease the base resistance (R/sub B/): a new base ohmic contact system of Ni/Ti/Pt/Ti/Pt for the low contact resistivity and an L-shaped base electrode for the low base electrode resistance. To our knowledge, this f/sub max/, value is the highest in GaAs based HBTs with the C-doped base layer. These techniques are very promising for high f/sub max/ HBTs with even the moderately doped base layer.