Si/Sige HETEROJUNCTION BIPOLAR TRANSISTORS (A REVIEW)

The research on Sı/SiGe heterojunction bipolar transisfors has led theultra-high-speed transıstors tha! are compatible wilh the state-of-the-art siliconinlegraled technology. The SiGe base regions ofthese transistors are grımn selectivetyon silicon substrates. Self-aligned slructures are used to reduce the external baseresisıance aııd base colleclor parasitic capacitance. The germanium profile in Ihe baseis graded to obtain a drift ejfect to reduce the base-transil tiıne. Si/SiGe integratedcircuils for applications in optical-flber link systems and Si/SiGe microwave poverIransistors have been produced wilh remarkable speeds. The SiGe semıconduaormaterial system, HBT slructures and fabricalion, and device performance issues arereviewed in thispaper.