Metal-induced gap states and Schottky barrier heights at nonreactive GaN/noble-metal interfaces

We present ab initio local density FLAPW calculations on nonreactive N-terminated [001] ordered GaN/Ag and GaN/Au interfaces and compare the results (such as metal induced gap states and Schottky barrier heights) with those obtained for GaN/Al, in order to understand the dependence of the relevant electronic properties on the deposited metal. Our results show that the density-of-gap states is appreciable only in the first semiconductor laver close to the interface. The decay length of the gap states in the semiconductor side is about 2.0+/-0.1 Angstrom and is independent of the deposited metal, therefore being to a good extent a bulk property of GaN. Our calculated values of the Schottky barrier heights are Phi(Bp) (GaN/Ag) = 0.87 eV and Phi(Bp) (GaN/Au) = 1.08 eV; both values are smaller than the GaN/Al Value [Phi(Bp) (GaN/Al) = 1.51 eV] and this quite large spread of values excludes the possibility of a Fermi-level pinning within the GaN band gap. Because of the low screening in GaN, the potential barrier at the junction is strongly affected by the structural arrangement of the first metal layer at the interface. This leads to quite large variations of the Schottky barrier height as a function of the metal. in contrast with the behavior of GaAs/metal interfaces.