Paper EM-TuP3
Rapid Thermal Ex-Situ Activation and Effect on Contacts to p-type GaN

Tuesday, October 19, 2010, 6:00 pm, Room Southwest Exhibit Hall

The difficulty of achieving ohmic contacts to p-type GaN is associated with the inherent difficulties involved in acceptor doping with Mg. Poor doping efficiency results in high contact resistance and high semiconductor sheet resistance. In GaN based devices, these issues lead to parasitic voltage drops and associated Joule heating. When grown via CVD methods a significant amount of Mg forms a complex with hydrogen. This complex prevents Mg from participating in active doping. The challenge is to achieve large concentrations of free Mg in the films. In-situ post-growth annealing has been found to enhance p-type conductivity, but there is a large disparity in activated Mg acceptors versus incorporated Mg atoms. Furthermore, we know of no reports in the literature regarding optimization of the annealing conditions. In this study we have conducted I-V, C-V, Hall, and contact resistance measurements of Ni/Au contacts on Mg-doped GaN films grown on AlN/SiC (0001) substrates as a function of annealing temperature and time, and nitrogen or oxygen concentration for in-situ and ex-situ anneals. We found that in-situ cooling in nitrogen after growth is important for initial activation of Mg dopants; however, additional in-situ annealing in nitrogen after growth had little effect on the electrical properties. We also found that the electrical characteristics are particularly sensitive to the presence of oxygen and temperature during ex-situ annealing; > 200% improvements in hole concentration were observed for annealing in 1:1 N₂:O₂ at 800°C. The electrical data will be correlated with SIMS data of the hydrogen concentration as a function of annealing conditions.