Microstructural and electrical investigation of Ni/Au ohmic contact on p-type GaN

Electrical properties of Ni/Au ohmic contacts on p-type GaN were interprete d with the change of microstructure observed under transmission electron mi croscopy. The contact resistivity was decreased from 1.3 x 10(-2) to 6.1 x 10(-4) Omega cm(2) after annealing at 600 degreesC. The reduction is due to the dissolution of Ga atoms into Au-Ni solid solution formed during anneal ing, via the generation of Ga vacancies, Thus, net concentration of holes i ncreased below the contact, resulting in the reduction of contact resistivi ty. At 800 degreesC, N atoms decomposed; reacted with Ni, and forming cubic Ni4N. Consequently, N vacancies, acting as donors in GaN, were generated b elow the contact, leading to the increase of contact resistivity to 3.8 x 1 0(-2) Omega cm(2).