High-Current Multi-Finger Mesa InGaAs/InP DHBTs

Characteristics of single- and multi-finger mesa InGaAs/InP double heterojunction bipolar transistors (DHBTs) are compared. The current gain decreases with the increasing number n_f of the emitter fingers due to the mutual thermal interaction between the fingers. The Kirk current can be as high as 150mA for four-finger DHBT. No degradation of the peak of the current gain cutoff frequency f_t is found for multi-finger DHBTs. The peak of the maximum oscillation frequency f_max decreases with an increase of n_f due to the increasing parasitic resistance of the base. The results are very helpful for applications of the common-base DHBTs in power amplifiers operating at very high frequencies.