Low-Resistive Ohmic Contacts for AlGaN Channel High-Electron-Mobility Transistors Using Zr/Al/Mo/Au Metal Stack

An AlxGa1-xN/AlyGa1-yN high-electron-mobility transistor (HEMT) with AlGaN as a channel layer has been fabricated on a sapphire substrate for high-output-power and high-frequency electronic applications. One of the key process steps for the AlGaN-channel HEMT is to ensure low resistivity for source/drain ohmic contacts. In this work, the electrical characteristics of Zr/Al/Mo/Au ohmic contacts for AlGaN-channel HEMTs were investigated at annealing temperatures from 850 to 1000 degrees C. An AlGaN-channel HEMT was fabricated with Al contents of 0.3 and 0.55 for the channel and barrier layer, respectively. A minimum ohmic contact resistivity of 2.6 x 10(-4) Omega cm(2) was achieved for the Al0.55Ga0.45N/Al0.3Ga0.7N heterostructure after annealing at 950 degrees C. (C) 2011 The Japan Society of Applied Physics