Si implant-assisted Ohmic contacts to GaN

The contact resistance, ρC, was measured for the traditional Ti/Al/Ni/Au Ohmic contact for samples implanted with Si to >1020 cm−3 and annealed at 1100, 1150, 1200, or 1250 °C for 2, 5 or 10 min using an AlN annealing cap. These results are compared with those for samples annealed in the same way, but were not implanted. The as-grown samples were doped to 3.56 × 1017 or 6.67 × 1016 cm−3 or were unintentionally (UI) doped. In almost all cases, ρC for the implanted sample was lower, and a record low ρC = 2.66 × 10−8 Ω cm2 was achieved for the more heavily doped implanted sample annealed at 1200 °C for 10 min. ρC decreased with the doping concentration, and for the UI samples, Ohmic contacts could be made only if the samples were implanted. The surface roughness was also measured, and it was found for an as-grown with an RMS roughness of 0.303 nm, the roughness increased from 0.623 after an 1100 °C anneal to 3.197 nm after a 1250 °C anneal for the implanted samples annealed for 10 min, and it increased from 1.280 nm to 5.357 nm under the same conditions for the samples that were not implanted.