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

Abstract

An Al x Ga 1- x N/Al y Ga 1- y N 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 °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 2.6×10 -4 Ω cm 2 was achieved for the Al 0.55 Ga 0.45 N/Al 0.3 Ga 0.7 N heterostructure after annealing at 950 °C.