Ohmic Contacts to implanted GaN

Ohmic contacts with low resistivity values to Si implanted GaN have been performed using a metal combination of Ti/Al. Different protection caps have been used during post-implantation annealing and their influences to the specific contact resistivity (rho_c) have been investigated. After the metal alloying, noticeable differences have been observed between the protected sample with SiO₂ and unprotected sample during the post-implantation annealing. The unprotected sample has shown lower values of rho_c but with very low reproducibility, while, by contrast, the use of SiO₂ cap has revealed the achievement of a low rho_c around 10^-5 Omega.cm² with very good uniformity. Based on the results obtained from electrical measurements, XRD (X-ray diffraction) analysis, AFM (atomic force microscopy) and SEM (scanning electron microscopy) observations, we discuss the mechanism for the uniformity in rho_c.