Ohmic Contact Mechanism of Titanium-based Electrodes on n-type Gallium Nitride

Electrical properties at the interface between n-type gallium nitride (GaN) and Ti-based contact layers formed by radio-frequency magnetron sputter deposition under various conditions were investigated to clarify the mechanism to achieve ohmic contacts. TiN contacts deposited using N2 gas are non-ohmic. Therefore, formation of TiN adjacent to GaN is not a necessary condition for achieving ohmic properties. On the other hand, Ti contacts deposited using Ar gas are ohmic in the as-deposited state, even though a layer of Ti2N is formed between GaN and Ti during the deposition. It is also shown that Ti deposition on undoped GaN produces ohmic contacts. The nitrogen vacancies increased in the sub-interface of GaN are essential for ohmic properties. The interfacial reaction between Ti and GaN to form nitrogen vacancies is affected by the partial pressure of N2 during the deposition.