Analysis on the new mechanisms of low resistance stacked Ti/Al Ohmic contact structure on AlGaN/GaN HEMTs

A novel stacked Ti/Al based Ti/Al/Ti/Al/Ti/Al/Ti/Al/Ni/Au Ohmic contact structure is optimized. Compared with the conventional alloyed Ti/Al/Ni/Au Ohmic contact structure, the novel Ohmic contact structure can obtain much lower contact resistance and specific contact resistivity. Through analysis of x-ray diffraction spectra, cross-section transmission electron microscopy images and corresponding electron dispersive x-ray spectroscopy spectra in the novel stacked Ti/Al based Ohmic structure, the reactions between metals and the AlGaN layer were proven to be stable, uniform and continuous, which produced smooth contact interface. In addition, the top Au layer was prevented from diffusing downwards to the metal/AlGaN interface, which degraded the Ohmic performance.