LOW-RESISTANCE OHMIC CONTACTS ON WIDE BAND-GAP GAN

We report a new metallization process for achieving low resistance ohmic contacts to molecular beam epitaxy grown n-GaN (approximately 10(17) 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-degrees-C in a N2 ambient using rapid thermal annealing techniques. The lowest value for the specific contact resistivity of 8X10(-6) OMEGA CM2, was obtained using Ti/Al metallization with anneals of 900-degrees-C for 30 s. X-ray diffraction and Auger electron spectroscopy depth profile were employed to investigate the metallurgy of contact formation.