Ti/Al/Ti/TiW Au-free low temperature ohmic contacts for un-doped AlGaN/GaN HEMTs

We demonstrated an Au-free ohmic contact for un-doped AlGaN/GaN HEMTs with Ti/Al/Ti/TiW metal structure. The Au-free ohmic contact was fabricated by pre-ohmic recess etching and low annealing temperature. The contact characteristics of the Ti/Al/Ti/TiW Au-free ohmic contacts including current-voltage, contact resistivity, and microstructure are systematically investigated. The contact resistivity of Ti/Al/Ti/TiW ohmic contact with 22-nm recessed depth and 600 °C annealing temperature is 5.44 × 10−5 Ω⋅cm2, which is comparable with conventional Ti/Al/Ni/Au ohmic contact. In addition, the Ti/Al/Ti/TiW ohmic contact shows smooth surface morphology with an excellent surface roughness of 3.69 nm. Besides, AlGaN/GaN MISHEMTs based on Ti/Al/Ti/TiW Au-free low temperature ohmic contacts were fabricated and exhibited good DC characteristics. The reported Au-free AlGaN/GaN HEMT fabrication process can be used in standard Si fabs without the risk of contamination.