Some ohmic contacts do rely on formation of metal-semiconductor phases (e.g. formation of Ni-Ga-O phase in case of Ni/Au contact on p-GaN). So it's important to identify the material you are interested in.
If it is Wurtzite GaN, the hexagonal arrangement of atoms is a clear evidence of c-plane. As in which c-plane (Ga-face or N-face) is beyond my knowledge. So you are viewing along the c-direction. Correct me if I'm wrong.