In this paper, we report the ohmic contact to n-GaN fabricated by implanting silicon into Mg-doped GaN using an
alloy of Ti/Al/Ti/Au metallization. The used materials were grown on (001) sapphire substrates by metal-organic
chemical-vapor deposition (MOCVD). The layer structure was comprised of a GaN buffer layer and followed by a 2 μm
thickness Mg-doped GaN (Na=5×1017cm-3) and then double silicon implantation was performed in order to convert
p-type GaN into n-type GaN films. The as-implanted samples were then thermal annealed at 1150 °C for 5 min in N2
ambient. The carrier concentration and Hall mobility were 3.13×1018 cm3 and 112 cm2/ (V·s) measured by Hall method.
Multilayer electrode of Ti (50 nm)/Al (50 nm)/Ti (30 nm)/Au (30 nm) was deposited on n-GaN using an electron-beam
evaporation and contacts were formed by a N2 annealing technique ranging from 600 to 900 °C. After annealing lower
than 700 °C, the contacts exhibited a rectifying behavior and became ohmic contact only after high temperature
processes (≥700 °C). Specific contact resistance was as low as 9.58×10-4 Ω·cm2 after annealing at 800 °C for 60 seconds.
While annealing temperature is higher than 800 °C, the specific contact resistance becomes worse. This phenomenon is
caused by the surface morphology degradation.
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