InP/InGaAs heterostructure bipolar transistors using a patterned subcollector

InP/InGaAs based heterostructure bipolar transistors (HBTs) have been fabricated using a process which starts with a patterned subcollector and subsequent regrowth aimed at achieving a lower base-collector capacitance. The n(+)-InGaAs subcollector layer was patterned using standard contact lithography and wet etching techniques. The remainder of the structure, collector, base and emitter, were then regrown over the patterned InGaAs. Small devices with an emitter size of 3x5 um(2) were fabricated and tested. RF measurements gave peak f(T), and f(max) values of 37GHz and 52 GHz respectively. These values were limited by a high collector resistance either due to the metal contact or possibly the initial regrowth interface. A minimum capacitance of 23 fF was measured at a bias of -2.2 V V-bc. This was about 20 % lower than for a standard processed device. These results indicate this type of regrowth process may provide a method for scaling devices smaller than is possible with standard mesa technology.