Analysis of surface roughness in Ti/Al/Ni/Au Ohmic contact to AlGaN/GaN high electron mobility transistors

Abstract

A mechanism of the formation of the bulges on the surface of Ti/Al/Ni/Au Ohmic contact in AlGaN/GaN high electron mobility transistors is proposed. According to the analysis of TEM images and corresponding electron dispersive x-ray spectra, the bulges were found to consist of Ni-Al alloy in the body and Au-Al alloy surrounding. We deduce that the bulges were formed due to Ni-Al alloy aggregation in some local areas during the rapid thermal annealing process, which accounts for the rough surface morphology