Electronic properties of polar and nonpolar InN surfaces: A quasiparticle picture

Using density-functional-based total-energy calculations and the LDA-1/2 method to compute approximately quasiparticle band structures, we have studied clean relaxed InN surfaces with varying polarity. More in detail, the $c$-plane, $a$-plane, and $m$-plane surfaces have been investigated. In contrast to the polar faces, which allow Fermi level pinning, the projected fundamental bulk gap of about 0.71 eV is free of surface states in the nonpolar cases. Consequently, freshly cleaved InN surfaces cannot lead to a surface accumulation layer. The different electronic structures modify the surface dipole and hence the ionization energy and electron affinity significantly when varying the surface normal from [0001] via [1$\overline{1}$00] or [11$\overline{2}$0] to [000$\overline{1}$].