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The physical mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures by laser annealing and rapid thermal annealing are systematically investigated. The microstructures indicate that a better surface morphology and an intact contact interface are formed after laser annealing. None of the TiN alloy spikes are formed at the interface of the laser annealing sample. The experimental results show that the current transport mechanism through the ohmic contact after laser annealing is different from the conventional spike mechanism, and it is dominated by thermionic field emission.

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The formation of ohmic contact in AlGaN/GaN high electron mobility transistor (HEMT) with low surface damage by selective laser annealing is reported. With selective laser annealing, the device exhibits a smaller sheet resistance, which is 74.9% of the device with the conventional rapid thermal annealing process. The dynamic ON-resistance is 1.35 times higher than the static ON-resistance after off-state drain voltage stress of 200 V, which benefits from the low surface defects using laser annealing. While the dynamic ON-resistance with rapid thermal annealing shows 8.66 times higher than the static ON-resistance after off-state drain voltage stress of 125 V. X-ray photoelectron spectroscopy analysis indicates that the AlGaN surface damage related to the oxidation reaction under the high-temperature condition is eliminated by using selective laser annealing, even in the air ambient.

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.

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