Development of Al-free ohmic contact to n-GaN

We have investigated the electrical properties and interfacial reactions of the Si/Ti-based ohmic contacts to Si-doped n-GaN grown by metal organic ch emical vapor deposition and the electrical properties were related to the m aterial reactions. Si/Ti contact system was selected because Ti silicides h ave a low work function comparable to Al and also Si was used widely as an n-type dopant. As the annealing temperature increased, the specific contact resistance of Si/Ti-based ohmic contacts decreased and showed minimum cont act resistance as low as 3.86 x 10(-6) Omega cm(2) after annealing at 900 d egreesC for 3 min under N-2 ambient. Our experimental results show that the ohmic behavior of Si/Ti-based contacts were attributed to the low barrier height of Ti-silicide/GaN interface, which was formed through the interfaci al reaction between Si and Ti layers. In order to clarify the current condu ction mechanism of Si/Ti-based contact, temperature dependent contact resis tance measurement was carried out for Au(1000 Angstrom)/Ti(400 Angstrom)/Si (1500 Angstrom)/Ti(150 Angstrom) contact system after annealing at 700 degr eesC for 3 min. The contact resistance of Si/Ti-based ohmic contact decreas ed exponentially with the measuring temperature and so it can be concluded that current flows over the low barrier height by thermionic emission.