TEM/HREM of Ti/Al and WNi/Ti/Al ohmic contacts for n-AlGaN

Abstract

High resolution and analytical transmission electron microscopy was applied to characterize the microstructure of Al/Ti and W/Al/Ti ohmic contacts to AlGaN/GaN HFET structures. Formation of a 15-25 nm thick interfacial AlTi/sub 2/N layer appears to be essential for ohmic contract behavior indicating a tunneling contact mechanism. Contact resistance was found to depend on the structure and composition of the metal and AlGaN layers, and on atomic structure of the interface. Contact resistivity increases with Al fraction in the AlGaN layer.