Tunneling at the emitter periphery in silicon-germanium HBTs

The low bias region of the base current has been studied in SiGe HBTs and s hown to arise from tunneling at the emitter periphery. Tunneling also descr ibes the reverse bias base-emitter current, which we believe is enhanced by mid-gap states. The reverse bias causes damage to the base-emitter region, increasing the base current. We also show that after a short period of sev ere reverse bias stress the base current displays random telegraph signals. These phenomena are often observed in silicon bipolar transistors, confirm ing that the incorporation of SiGe has not produced any other undesirable c haracteristics.