  We present ab-initio local density FLAPW calculations on non-reactive
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 layer close to the
interface. The decay length of the gap states in the semiconductor side is
about 2.0 $\pm$ 0.1 \AA $\:$ 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 $\Phi_{B_p}(GaN/Ag)$ = 0.87 eV and
$\Phi_{B_p}(GaN/Au)$ = 1.08 eV; both values are smaller than the GaN/Al value
($\Phi_{B_p}(GaN/Al)$ = 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.
