Control of interface states at metal/6H-SiC(0001) interfaces

Metal/6H-SiC(0001) interfaces free of Fermi level pinning were formed by realizing well-ordered atomic arrangements and perfect termination of the surface atoms of SiC substrates. The surfaces and interfaces were investigated by electrical measurements, Auger electron spectroscopy, low energy electron diffraction, x-ray photoemission spectroscopy, scanning tunneling microscopy, and transmission electron microscopy. We used three different regimes for the surface treatments: ~i! the conventional procedure of degreasing and HF dipping, ~ii ! thermal oxidation followed by HF dipping after ~i!, and ~iii ! immersion into boiling water after ~ii !. We found that the dependence of the Schottky barrier height on the metal work function changes drastically following these surface treatments. The Fermi level at the interface prepared using only treatment ~i! was almost pinned at ;0.8 eV below the conduction band minimum. On the other hand, for the interfaces formed by treatments~ii ! and ~iii !, the position of the interface Fermi level varied strongly with the metal work function. In particular, treatment ~iii ! approached the Schottky limit, with a density of interface states of 4.6 310 states•cm•eV. The surface characterization of the SiC surfaces formed by the Schottky-limit treatment~iii ! indicated that the surface was atomically flat, the terraces of the surface was terminated by hydrogen atoms, and their step-edges were stable due to passivation by oxygen. An abrupt commensurate epitaxial connection at the Ti/SiC interface was found for treatment ~iii !, whereas the Ti/SiC interface obtained by employing treatment ~i! had a disordered layer with a thickness of ;2 nm, which is the origin of the large density of interface states enough to pin the interface Fermi level.

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