Improved Thermal Stability and Reduced Contact Resistance of Ohmic Contacts on N-Face n-Type GaN With Laser-Assisted Doping

The authors report reduced contact resistance and improved thermal stability of Ti/Al ohmic contacts to N-face n-GaN via laser-assisted Si doping. The contact resistivity of Ti (30 nm)/Al (200 nm) electrodes was reduced from 7.61 x 10(-4) to 8.72 x 10(-5) Omega . cm(2) by applying laser-assisted Si diffusion to the GaN surface before Ti/Al deposition. Moreover, no degradation in specific contact resistivity was observed for the highly doped samples after annealing at 300 degrees C. During this process, Si dopant atoms are believed to diffuse into GaN, whereas Ga-N bonds are broken by laser-assisted doping, which eventually increases the number of nitrogen vacancies and generates sites at which Si atoms are substituted for Ga on the GaN surface. This suggestion was verified by secondary ion mass spectrometry and X-ray photoelectron spectroscopy.