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Silicon Carbide Emitter NPN Bipolar Transistors

(by Dr. Fred Ruddell)

These SEM images show NPN bipolar transistors fabricated as part of a Research Council project which demonstrated the use of silicon carbide (SiC) as the emitter material in a silicon-based heterojunction bipolar transistor (HBT).  SiC has a relatively wide bandgap of 2.2eV, and it exhibits high thermal stability, controllable conductivity, and high electron saturated drift velocity.  This project avoided the high thermal budgets often associated with SiC deposition by employing Rapid Thermal Processing (RTP) to grow in-situ doped SiC layers using silane (SiH₄), propane (C₃H₈) and phosphine (PH₃) gas chemistry.  The purpose-built RTP reactor also included the facility to perform in-situ silicon surface cleans using microwave plasma etching.  The SiC NPN bipolar transistors fabricated using this technique displayed increased common-emitter current gain compared to standard devices, which was directly attributable to the action of the heterojunction emitter.