Passivated InGaP/GaAs heterojunction bipolar transistor technology using Pt/Ti/Pt/Au base contacts

We have developed a fully-passivated, self-aligned, thermally-shunted InGaP/GaAs HBT by alloying the base contact (Pt/Ti/Pt/Au) through the thin InGaP emitter layer. The dc current gain (β) was increased from 45 to 92 at a current density of 25 kA/cm ² on devices from the same wafer. Also, the decrease in β with increasing emitter periphery/area ratio was reduced. Furthermore, the device´s rf performance was not degraded. A cutoff frequency (f_t) of 40 GHz at a collector current density (J _c) of 25 kA/cm² was demonstrated. The base contact process was used on wafers with 150, 250 and 350 Å InGaP emitters. The best base contact resistance obtained was 0.05 Ω-mm with the 200 Å Pt:200 Å Ti:500 Å Pt:1300 Å Au metallization