Microwave performances of n.p.n. and p.n.p. AlGaAs/GaAs heterojunction bipolar transistors

The performances of metalorganic vapor-phase-deposition (MOCVD)-grown heterojunction bipolar transistors (HBTs) were compared at microwave frequencies to identify relative merits of each type of device. Figure-of-merit (ft) and maximum frequency of oscillation (f/sub max/) values of devices with 100-nm-thick bases were 22 and 40 GHz for n-p-n transistors, and 19 and 25 GHz for p-n-p transistors, respectively. An accurate device model was developed using the measured S-parameter data. The base resistance of the p-n-p transistors, as determined from the model, was about five times lower than identical-size n-p-n devices. A theoretical comparison of the two types indicates that similar performances may be obtained from both if the base layer thickness of p-n-p transistor is half that of the n-p-n device. Large-signal characterization was carried out at 10 GHz.<>