GaN, one of III-Nitrides with wide band gap of 3.4eV can emitt light from the range of blue to ultra-violet. This material has been receiving great attention as a potential material for the application of blue LED and LDs. Unlike the other competitors, this is highly stable even at high temperature operation and is very inert to chemicals due to strong nitrogen bond.
In the present study, ohmic contact characteristics of various contact materials on Mg doped p-type GaN were studied. For this purpose two MBE grown Mg doped GaN with different doping concentration level, one with $10^{19}/㎤$ and the other $10^{16}/㎤$ were used. As the contact materials Cr/Au, Pt/Au, Ti/Pt/Au multilayered metal films were fabricated by a conventional lift-off process. Contact properties were analyzed by measuring specific contact resistances and TLM(Transmission Line Method) was employed to measure the specific contact resistance.
The specific contact resistance of the p-GaN and the different multilayered metal films were measured in as-deposited state and after rapid thermal annealing for one minute. Among the specimens, the specimen deposited with Cr/Au on $p^+$-GaN and annealed at 500℃ for 1min showed the lowest specific contact resistance of $1.2×10^{-4}$ ohm-㎠, which is believed the lowest value ever reported in p-GaN.
SAM(Scanning Auger Microscope) and glancing angle XRD were used to understand the interface between the metal and p-GaN. The results showed Cr diffusion into the p-GaN side, which is believed as the origin of the low specific contact resistance.
