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 chemical vapor deposition and the electrical properties were related to the material reactions. Si/Ti contact system was selected because Ti silicides have 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 contact resistance as low as 3.86 x 10 super(-6) Omega cm super(2) after annealing at 900 degree C for 3 min under N sub(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 interfacial reaction between Si and Ti layers. In order to clarify the current conduction mechanism of Si /Ti-based contact, temperature dependent contact resistance measurement was carried out for Au(1000 A)/Ti(400 A)/Si(1500 A) /Ti(150 A) contact system after annealing at 700 degree C for 3 min. The contact resistance of Si/Ti-based ohmic contact decreased exponentially with the measuring temperature and so it can be concluded that current flows over the low barrier height by thermionic emission.