The work investigates an increase of the density of free charge carriers in the sub-surface region of p-GaN by adding p-type dopants into the Ni-O layer of an Au/Ni-O metallization structure. We have examined electrical properties and concentration depth profiles of contact structures Au/Ni-Mg-O/p-GaN and Au/Ni-Zn-O/p-GaN, thus with magnesium and zinc as p-type dopants. The metallization layers were deposited on p-GaN by DC reactive magnetron sputtering in an atmosphere with a low concentration of oxygen (0.2 at%). The contacts were annealed in N2 . We have found that the structures containing magnesium or zinc exhibit lower values of contact resistivity in comparison with otherwise identical contacts without Mg or Zn dopants. In our opinion, the lower values of contact resistivity of the structures containing of Mg or Zn are caused by an increased density of holes in the sub-surface region of p-GaN due to diffusion of Mg or Zn from the deposited doped contact layers.