Ab initiocalculations of SiC(110) and GaAs(110) surfaces: A comparative study and the role of ionicity

Abstract

We report ab initio calculations of structural and electronic properties of P-SiC and of the nonpolar SiC(110) surface. The calculations are carried out self-consistently in the local-density approximation employing smooth norm-conserving pseudopotentials in separable form. Gaussian orbital basis sets are used for an efficient description of the wave functions. These are strongly localized at the carbon atoms, in particular. For the bulk crystal 40 Gaussians per unit cell with s, p, d, and s symmetry are found to be sufficient for good convergence. Our results for the SiC ground-state structural parameters and the bulk band structure are in excellent agreement with the results of previous plane-wave calculations and with experimental data. We scrutinize the character of the chemical bond in SiC by comparisons with diamond, Si, GaAs, and ZnS, which have been investigated on equal footing. The SiC(110) surface is described in a supercell geometry. The optimal surface relaxation is determined by eliminating the forces iteratively. We And a top-layer bond-length-contracting rotation relaxation in which the Si surface layer atoms move closer towards the substrate while the C surface-layer atoms relax only parallel to the ideal surface plane. SiC(110) exhibits an occupied and an empty dangling-bond band within the fundamental gap. The occupied band predominantly originates from the dangling bonds at the surface carbon atoms which behave like anions. The empty band mainly originates from the dangling bonds at the surface Si atoms which act as cations. We present and discuss our results for the SiC(110) surface in direct comparison with the GaAs(110) surface. Further comparisons with literature data on surfaces of more ionic II-VI compounds like ZnS or ZnO are given, as well. This allows us to address the physical origins of the surface relaxation behavior of these compound semiconductors and to identify characteristic di6'erences and similarities in the relaxation which are related to the specific types of heteropolarity or ionicity of these systems.

Theoretical study of magnetic moments induced by defects at the SiC(110) surface

“…As in Ref. 11, we obtain a nonmetallic surface with two well-separated surface bands (see Fig. 1); the occupied narrow one is mainly owing to the C dangling bond, whereas the unoccupied wider one has a Si character, as the projected densities of states reveals (see Fig.…”

“…We find a partially ionic Si-C bond with a charge transfer of 0.45 electrons to the Si atom as evaluated using a Mulliken population analysis. We obtain a band gap of 1.31 eV, similar to the 1.29 eV band gap calculated by Sabisch et al 11 and to be compared to the experimental one of 2.417 eV. 21 To simulate the free SiC(110) surface we have performed calculations of slabs formed by the stacking of (110) planes with different sizes.…”

“…2). We, as Sabisch et al, 11 obtain a buckled nonreconstructed surface; the C and Si atoms are displaced normal to the surface by 0.01Å outward and by 0.24Å inward, respectively. Surface bonds are shorter (1.81Å) than the bulk ones (1.91Å) and bond angles (∼122…”

“…The free SiC(110) surface has been theoretically studied by Sabisch et al 11 (for a complete review of the different SiC surfaces, see Ref. 12).…”

Defects in III-V semiconductor surfaces

“…It has been suggested that the preferred planar threefold coordination with occupied sp 2 -like and empty p z -like orbitals at the group-III atoms and the three-dimensional (incomplete) tetrahedral coordination with sp 3 -like orbitals at the group-V atoms are the driving forces of the relaxation [6][7][8][9].…”