Au/Pt/Ti/Pt base contacts to n-InGaP/p+-GaAs for self-passivating HBT ledge structures

Multi-layer ohmic contact systems such as Au/Pt/Ti/Pt on III-V double layers such as n-InGaP/p(+)-GaAs are of considerable technological relevance, e.g. for heterojunction bipolar transistors. The paper shows that such contacts can be effectively reacted through the InGaP layer and exhibit very good contact resistances (0.1 Omega mm) to the base layer if the thickness of the first Pt layer is properly marched to the thickness of the contacted InGaP layer. Interdiffusion and phase formation associated with the annealing processes are studied by cross-sectional analytical transmission electron microscopy, thin-film x-ray diffraction and Auger electron spectroscopy depth profiling. Thermal ageing experiments up to 400 degrees C show good electrical stability. Device related reliability tests do not show any degradation effect related to this novel base contact.