Ohmic contacts to Si-implanted and un-implanted n-type GaN

We report on ohmic contacts to Si-implanted and un-implanted n-type GaN on sapphire. A ring shaped contact design avoids the need to isolate the contact structures by additional implantation or etching. Metal layers of Al and Ti/Al were investigated. On un-implanted GaN, post metalization annealing was performed in an RTA for 30 seconds in N{sub 2} at 700, 800, and 900 C. A minimum specific contact resistance (r{sub c}) of 1.4{times}10{sup -5} {Omega}{minus}cm{sup 2} was measured for Ti/Al at an annealing temperature of 800 C. Although these values are reasonably low, variations of 95% in specific contact resistance were measured within a 500 {mu}m distance on the wafer. These results are most likely caused by the presence of compensating hydrogen. Specific contact resistance variation was reduced from 95 to 10% by annealing at 900 C prior to metalization. On Si-implanted GaN, un-annealed ohmic contacts were formed with Ti/Al metalization. The implant activation anneal of 1120 C generates nitrogen vacancies that leave the surface heavily n-type, which makes un-annealed ohmic contacts with low contact resistivity possible