Improvement of Au‐Free, Ti/Al/W Ohmic Contact on AlGaN/GaN Heterostructure Featuring a Thin‐Ti Layer and Low Temperature Annealing

Abstract

In this study, a Ti/Al/W ohmic contact and the factors that determine the optimal annealing temperature are investigated to obtain Au‐free high‐electron mobility transistor (HEMT) with a low thermal budget. The results show that a thin‐Ti layer of 2.7 nm with a low specific contact resistance of 2.54 × 10−6 Ω · cm2 (0.358 Ω mm) is realized in 10 min at a low annealing temperature of 500 °C. It is found that a thinner Ti layer leads to a lower annealing temperature because Al needs to diffuse through the Ti layer and make contact with AlGaN to obtain linear I–V characteristics. In addition, Ti is essential in removing the natural oxide film on AlGaN surface, and the minimum thickness of the Ti layer is 2 nm. The Au‐free AlGaN/GaN HEMT on a silicon wafer shows comparable characteristics with the conventional Au‐containing HEMT, which leads to low cost manufacturing of HEMTs in existing silicon‐device fabrication lines.