Millimeter-wave AlGaAs/GaAs p-n-p HBT

The total emitter-to-collector delay for a p-n-p AlGaAs/GaAs heterojunction bipolar transistor (HBT) has been reduced to 5.7 ps by extending the cutoff frequency for these devices to the millimeter-wave range. A total charging delay of 1.2 ps was obtained by a lightly doped emitter and by reducing the collector resistance. Low transit delays totaling 4.5 ps were achieved with a thin (440 Å) uniformly doped base and a thin (2800 Å) collector. The reduction in these delays permitted a non-self-aligned (1-μm emitter mesa/base contact separation) device with two emitters (2.6×10 μm² each) and a single base contact to exhibit an f_t of 28 GHz