Low-resistance Ti/Al/Ti/Au multilayer ohmic contact to n-GaN

A metallization scheme has been developed for obtaining low ohmic contacts to n-GaN with a low contact resistance. The metal contact is a Ti/Al/Ti/Au composite with layers that are respectively 30, 100, 30, and 30 nm thick. C ontacts with a specific contact resistivity rho (s), as low as 6.0x10(-7) O hm cm(2) for a doping level of 1.40 x 10(20) cm(-3) were obtained after ann ealing the sample for 30 s at 750 degreesC in a rapid thermal annealer. The Ti placed on top of the traditional Ti/Al contact appears to have the adva ntage of tying up the excess Al; therefore it does not form a mottled conta ct. Some of the additional Ti-Al intermetallic alloys that are formed also have beneficial effects. The Ti-Au layer forms a robust upper portion of th e composite, which enables the contacts to have high-temperature applicatio ns. (C) 2001 American Institute of Physics.