Valence electronic structure of polycrystalline SiC as observed by (e,2e) spectroscopy

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Abstract
The spectral momentum density ρ(ε,q) of the valence electrons of a thin polycrystalline silicon carbide (SiC) film has been measured using an (e,2e) spectrometer employing a noncoplanar asymmetric geometry with estimated energy and momentum resolutions of about 2.0 eV and 0.15 a.u., respectively. Well-defined valence-band dispersion has been observed from the measured momentum density which resembles a parabola, but deviates from what is expected for a free electron near the top of the band and at the boundary of the Brillouin zone, where the antisymmetric gap due to the unequal potentials between the Si and C sites in SiC is clearly visible. Based on the assumption that the spectral momentum density of polycrystalline materials is a spherical average of the spectral momentum density of the corresponding single crystalline phase of the materials, ab initio linear muffin-tin orbital calculations have been performed using the zinc-blende structure of β-SiC. The measured dispersion of the energy band is in excellent agreement with theory. Reasonable agreement is also obtained for the energy-integrated momentum density, although the measured momentum density exceeds considerably the calculated one at high momenta. The theoretical implication of using crystal band-structure calculations for studying disordered materials is also discussed.