Improved AlGaAs/GaAs HBT performance by InGaAs emitter cap layer

The effects of the emitter resistance reduction on the DC and high-frequency characteristics in an AIGaAs/GaAs HBT with an InGaAs emitter cap layer are investigated. In fabricated devices, a transconductance per unit area of 16mS/?m2 and a cutoff frequency of 80 GHz have been achieved.