Ohmic contact on low-doping-density p-type GaN with nitrogen-annealed Mg

We have demonstrated a fabrication process for the Ohmic contact on low-doping-density p-type GaN with nitrogen-annealed Mg. An Ohmic contact with a contact resistance of 0.158 omega cm(2) is realized on p(-)-GaN ([Mg] = 1.3 x 10(17) cm(-3)). The contact resistance of p-type GaN with higher Mg concentration ([Mg]=1.0 x 10(19) cm(-3)) can also be reduced to 2.8 x 10(-5 )omega cm(2). A localized contact layer is realized without any etching or regrowth damage. The mechanism underlying this reduced contact resistance is studied by scanning transmission electron microscopy with energy dispersive x-ray spectroscopy and secondary ion mass spectrometry, representing a mutual diffusion of Ga and Mg atoms on the interface. Reductions in the barrier height and surface depletion width with the nitrogen-annealed Mg layer are confirmed by XPS and Hall effect measurements qualitatively.