ZnSe/GaAs heterostructure bipolar transistors: design and operation of a new II-VI/III-V device structure

A report is presented on the fabrication and measurement of ZnSe/GaAs heterostructure bipolar transistor (HBT) device structures. Using a wide-gap emitter allows increased design flexibility since it decouples constraints between the base doping and emitter injection efficiency. The ZnSe/GaAs interface is ideal since it provides a large barrier in the valence band for the holes, but only a small barrier in the conduction band for the electrons. This combination of band offsets guarantees the back injected base current will be small independently of the base doping. In addition, the lattice mismatch is small (0.27%). Combining II-VI/III-V materials opens up to a new class of device possibilities. Results are presented for the ZnSe/GaAs HBT device structures. Increased optimization of the structure and more mature processing technology should improve device characteristics further.