Low resistance ohmic contacts on wide band-gap GaN

Abstract

We report a new metallization process for achieving low resistance ohmic contacts to molecular beam epitaxy grown n-GaN (∼1017 cm−3) using an Al/Ti bilayer metallization scheme. Four different thin-film contact metallizations were compared during the investigation, including Au, Al, Ti/Au, and Ti/Al layers. The metals were first deposited via conventional electron-beam evaporation onto the GaN substrate, and then thermally annealed in a temperature range from 500 to 900 °C in a N2 ambient using rapid thermal annealing techniques. The lowest value for the specific contact resistivity of 8×10−6 Ω cm2, was obtained using Ti/Al metallization with anneals of 900 °C for 30 s. X-ray diffraction and Auger electron spectroscopy depth profile were employed to investigate the metallurgy of contact formation.