Ab initio study of interface states and Schottky barriers at metal contacts to GaN(001)

Abstract

Using first-principles pseudopotential calculations, we investigated the nature of electronic states with energies in the semiconductor band gap of several abrupt, defect-free, N-terminated metal/GaN(001) junctions. In particular, the electronic structure of Al, Au and Cu junctions to cubic GaN(001) was investigated. The calculated Schottky barriers are 0.82 eV for Au/GaN(001), 1.0 eV for Cu/GaN(001) and 1.6 eV for Al/GaN(001). At these contacts, resonant and localized intermetallic interface states occur under the condition that atoms on the outermost atomic plane of the metal are placed in front of the outermost semiconductor cation. Similar states have been reported earlier for As-terminated Al/GaAs(001) and Al/AlAs(001) junctions [1,2] indicating that the formation mechanism of these states is a very general one. We have shown that these interface states derive from an interaction between localized states of the metal(001) surface and semiconductor conduction band states, mediated by localized states of the unreconstructed semiconductor(001) surface. In contrast to Al/AlxGa1–xAs junctions, where the midgap region is dominated by these states, they occur at energy much larger than the Fermi energy EF for the contacts to GaN. Thus, they are not expected to contribute significantly to the electronic transport of the latter interfaces. A large number of interface states attributed to d-type orbitals, however, occur over a wide energy range including EF at contacts of noble metals to GaN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)