Integration of a superlattice limiter into the HBT emitter for improved operational reliability

A common problem limiting the output power of multiple finger heterojunctio n bipol ar transistors (HBT's) is nonuniform current flow in the fingers, r esulting from an underlying nonuniform temperature distribution. We have fa bricated HBT devices containing an integrated superlattice region to help o vercome this problem,We demonstrate that the superlattice functions as a te mperature-dependent resistive current limiter in a single finger device at de and RF. Furthermore, the RF performance of the HBT was not compromised b y the inclusion of the superlattice structure.