Investigation of Fermi level pinning at semipolar (11–22) p-type GaN surfaces

• Dependence of SBH on metal work functions at semipolar (11–22) p-GaN surfaces is studied.
• SBH increases with temperature, whereas the ideality factor decreases.
• Temperature dependence of SBH and ideality factor explained by the barrier inhomogeneity model.
• The surface Fermi level is almost perfectly pinned at deep-level states.

Schottky barrier height (SBH; ΦB) and their dependence on the work function of metals (ΦM) at semipolar (11–22) p-GaN surfaces were investigated using Schottky diodes fabricated with different metals. The SBH increased with temperature, whereas the ideality factor decreased. This behavior was explained by means of the barrier inhomogeneity model, giving the mean barrier heights of 1.93–2.05 eV for different metals. The S-parameter (dΦB/dΦM) was obtained to be 0.04. This small S-parameter implies that the surface Fermi level is nearly perfectly pinned at deep-level states (caused by vacancy-related and/or Mg-induced defects) located at 1.98 eV above the valence band. This finding indicates that the surface modification is essentially required for the formation of high-quality ohmic and/or Schottky contacts.