Ohmic contacts to n-type GaN

Ohmic contacts to n-GaN using, Ag, Au, TiN, Au/Ti, Au/Mo/Ti, and Au/Si/Ti have been studied. The Fermi level of GaN appears to be unpinned, and metals and compounds with work functions less than the electron affinity resulted in ohmic contacts. Reactively sputter deposited TiN was ohmic as deposited. However, Au/Ti, Au/Mo/Ti, and Au/Si/Ti required heat treatments to form ohmic contacts, with the best being an RTA at 900 degrees C. Ag and Au were shown to diffuse across the GaN surface at T>500 degrees C; therefore, they are unstable, poor ohmic contact metallizations as single metals. The other contact schemes were thermally stable up to 500 degrees C for times of 30 min.