Ohmic contacts to n+-GaN capped AlGaN∕AlN∕GaN high electron mobility transistors

Investigations of Ti∕Al∕Mo∕Au Ohmic contact formation, premetallization plasma treatment effects, and interfacial reactions for n+-GaN capped AlGaN∕AlN∕GaN heterostructures are presented. Ti thickness played an important role in determining contact performance. Transmission electron microscopy studies confirmed that thick Ti layer was necessary to fully consume the GaN cap and the top of AlGaN to enable a higher tunneling current flow. A direct correlation of plasma treatment conditions with I-V linearity, current level, and contact performance was established. The plasma-affected region is believed to extend over 20nm into the AlGaN and GaN.