Protection of isolated and active regions in AlGaN/GaN HEMTs using selective laser annealing

AlGaN/GaN high-electron-mobility transistors with Au-free ohmic contacts are fabricated by selective laser annealing and conventional rapid thermal annealing. The current transport mechanism of ohmic contacts is investigated. High-temperature annealing can be avoided in the isolated region and the active region by selective laser annealing. The implanted isolation leakage current is maintained 10^-6 mA/mm even at 1000 V after selective laser annealing. On the contrary, high-temperature annealing will cause obvious degradation of the isolation. The morphology of AlGaN surface is measured by atomic force microscope. No noticeable change of the AlGaN surface morphology after selective laser annealing, while the root-mean-square roughness value markedly increases after rapid thermal annealing. The smaller frequency dispersion of capacitance-voltage characteristics confirms the lower density of surface states after selective laser annealing. Thus, dynamic on-resistance is effectively suppressed.