Low resistivity contacts to p-type GaN by plasma treatment

A N-2-based plasma has been applied to a p-type GaN surface in order to improve contact resistivity. It has been found that the dc bias voltage of the plasma, which dictates the energies of incident ions, plays an important role in the effectiveness of the treatment. A reduction of contact resistivity has been achieved with a plasma of -75 V de bias voltage. Excessive ion energies result in a deterioration of the contacts, as a result of plasma damage. The result is supported by XPS data, where a decrease of contact resistivity is linked to a shift of the binding energy of the Ga 3d core level towards lower energies. Such a shift indicates a reduction of the surface band bending coincident with an decrease of the surface barrier height, giving rise to a decrease contact resistance.