Anisotropic hole transport along [0001] and [11 2 ¯0] direction in p-doped (10 1 ¯0) GaN

The anisotropic hole transport along [0001] and [11 2 ¯0] in the p-doped (10 1 ¯0) GaN layer was compared for layers grown on bulk (10 1 ¯0) GaN substrates and on (10 1 ¯0) sapphire. The sheet resistance along [0001] was 1.1 times larger on GaN substrates and even 1.2 times larger on sapphire than that along [11 2 ¯0]. The anisotropic hole transport on bulk GaN substrates is due to the anisotropy of the hole’s effective mass and the different contribution of carriers in different bands, whereas the larger anisotropy for GaN on sapphire is also due to additional scattering at stacking faults. The annealing process of metal Mg applied to the m-plane p-type GaN successfully results in a robust p-type ohmic contact, functioning as a p + + layer.