Analyses of ohmic contacts to GaAs based microwave HBTs

Summary form only given. We compare the electrical, physical, and chemical properties of TiPdAu and PdGeTiPt contacts for GaAs HBTs. Contact and specific contact resistances are measured using the TLM method and devices made with the two different types of emitter contacts are compared, the surface structures are examined using optical and scanning electron microscopy, and the chemical structures are investigated with Auger and transmission electron microscopy. In addition, comparisons are made between the TiPdAu and PdGeTiPt contacts to heavily C-doped GaAs. The advantages of being able to substitute PdGeTiPt contacts for TiPdAu are that all of the contacts could be made with a single metallization, and the Pt would be a more effective diffusion barrier to the in-diffusion of Au.