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

Abstract

Metal/$6\mathrm{H}\ensuremath{-}\mathrm{SiC}(0001)$ 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 \ensuremath{\sim}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 $4.6\ifmmode\times\else\texttimes\fi{}{10}^{10}{\mathrm{states}\mathrm{\ensuremath{\cdot}}\mathrm{cm}}^{\ensuremath{-}2}\ensuremath{\cdot}{\mathrm{eV}}^{\ensuremath{-}1}.$ 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 \ensuremath{\sim}2 nm, which is the origin of the large density of interface states enough to pin the interface Fermi level.