Low Specific Contact Resistivity of 10−3Ω·cm2 for Ti/Al/Ni/Au Multilayer Metals on SI-GaN:Fe Substrate

For the application of third-generation compound semiconductors based on high-voltage, high-power, and high-frequency devices, particularly in photoconductive semiconductor switches (PCSSs), the ohmic contact preparation technology on semi-insulating substrates is crucial. However, iron-doped semi-insulating gallium nitride (SI-GaN:Fe) with low carrier concentration and high bulk resistivity has a very difficult time achieving good ohmic contact characteristics. Here, we have demonstrated preliminary results on an interesting class of good ohmic contact of Ti/Al/Ni/Au on Ga-face of SI-GaN:Fe. The results indicated that the Ti and Al thickness ratio is a critical parameter when determining the optimum annealing temperature and time for ohmic contact. With alloyed Ti/Al/Ni/Au stacks of 20 nm/120 nm/55 nm/45 nm on SI-GaN:Fe after annealing at 850 °C for 35 s in N2 atmosphere, a low specific contact resistivity of $10^{-3}\,\,\Omega \cdot $ cm2 is achieved. At a future date, such excellent ohmic contact characteristics can be applied to the SI-GaN:Fe-based high-power PCSS.