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 (/spl beta/) was increased from 45 to 92 at a current density of 25 kA/cm/sup 2/ on devices from the same wafer. Also, the decrease in /spl beta/ with increasing emitter periphery/area ratio was reduced. Furthermore, the device's rf performance was not degraded. A cutoff frequency (f/sub t/) of 40 GHz at a collector current density (J/sub c/) of 25 kA/cm/sup 2/ was demonstrated. The base contact process was used on wafers with 150, 250 and 350 /spl Aring/ InGaP emitters. The best base contact resistance obtained was 0.05 /spl Omega/-mm with the 200 /spl Aring/ Pt:200 /spl Aring/ Ti:500 /spl Aring/ Pt:1300 /spl Aring/ Au metallization.