Direct contact mechanism of Ohmic metallization to AlGaN/GaN heterostructures via Ohmic area recess etching

The effects of recess etching of the Ohmic contact area on the performance of Ti/Al/Mo/Au metallization and its interfacial reactions with AlGaN/AlN/GaN epilayers were investigated. The best Ohmic contact performances of 0.31, 0.41, and 0.26 Ω mm for three epilayers from two different sources were obtained only when the two-dimensional electron gas (2DEG) channels were completely removed under the Ohmic contact metallization. This is due to the direct sideway contact made by the electrode to the 2DEG around the edges of the active-layer mesas or pads; this is believed to be a more efficient carrier transport mechanism than tunneling through the AlGaN barrier.