We report on a first-principles study of all the structurally different stacking faults that can be introduced by elide along the (0001) basal plane in 3C-, 4H-, and 6H-SiC based on the local-density approximation within the density-functional theory. Our band-structure calculations have revealed that both types of stacking faults in 4H-SiC and two of the three different types of stacking faults in 6H-SiC give rise to quasi-two-dimensional energy band states in the band gap at around 0.2 eV below the lowest conduction band, thus being electrically active in n-type material. Although stacking faults, unlike point defects and surfaces, are not associated with broken or chemically perturbed bonds, we find a strong localization, within roughly 10-15 Angstrom perpendicular to the stacking fault plane, of the stacking fault gap state wave functions. We find that this quantum-well-like feature of certain stacking faults in SiC can be understood in terms of the large conduction-band offsets between the cubic and hexagonal polytypes. Recent experimental results give qualitative support to our results.

A first-principles calculation of stacking fault energies in 3C-, 4H-, and 6H-SiC, based on the local-density approximation within the density-functional theory, is reported. All the structurally different stacking faults which can be introduced by glide along the (0001) basal plane are considered. The number of such stacking faults in these polytypes is one, two, and three, respectively. The stacking fault energies are also calculated using the simpler generalized axial next-nearest-neighbor Ising (ANNNI) model. Our calculations confirm that the stacking fault energy of 3C-SiC is negative, and we also find that one of the three types of stacking faults in 6H-SiC has a considerably higher stacking fault energy than the other two types.

The multiple stacking faults in 4H-SiC, leading to narrow 3C polytype inclusions along the hexagonal c direction, were discussed. The stacking fault energies for successive stacking faults were calculated. The analysis showed that the stacking fault energy for the two stacking faults in adjacent basal planes was reduced by approximately a factor of 4 relative to that of one isolated stacking fault.

We report on a theoretical investigation of extended planar defects in 3C-, 4H-, 6H-, and 15R-SiC which can be formed without breaking any bonds, covering a wide range of planar defects: twin boundaries, stacking faults, and polytype inclusions. Their electronic structures have been intensively studied using an ab initio supercell approach based on the density functional theory. Stacking fault energies are also calculated using both the supercell method and the axial next-nearest-neighbour Ising model. We discuss the electronic properties and energies of these defects in terms of the geometrical differences of stacking patterns.

Recent attempts to make SiC diodes have revealed a problem with stacking fault expansion in the material, leading to unstable devices. In this paper, we present detailed results from a density-functional supercell calculation on the electronic structure of stacking faults which result from glide of Shockley partials in 3C-, 4H- and 6H-SiC. It was found [Phys. Rev. B 65, 033203 (2002)] that both types of stacking faults in 4H-SiC and two types of stacking faults in 6H-SiC give rise to band states, which are strongly localized (confined within around 10 Angstrom) in the direction orthogonal to the stacking fault plane. Based on estimates of the band offsets between different polytypes and a simple quantum-well theory, we show that it is possible to interpret this one-dimensional localization as a quantum-well confinement effect. We also find that the third type of stacking fault in 6H-SiC and the only stacking fault in 3C-SiC do not give rise to states clearly separated from the band edges, but instead give rise to rather strongly localized band states with energies very close to the band edges. We argue that these localized near band edge states are created by stacking fault induced changes in the dipole moment associated with the hexagonal symmetry. In addition, we have also calculated the stacking fault energies, using both the supercell method and the simpler ANNNI (axial next nearest-neighbor Ising) model. Both theories agree well with the low stacking fault energies found experimentally.

A first-principles calculation of stacking faults in 15R-SiC is reported. All the geometrically distinguishable stacking faults which can be introduced by the glide of partial dislocations in (0001)-basal planes are investigated: there exist as many as five different stacking faults in 15R-SiC. Electronic properties and stacking fault energies of these extended defects are studied based on the density functional theory in the local density approximation. Stacking fault energies are also calculated using the axial next nearest neighbor Ising (ANNNI) model.

A ab initio study of 3 C inclusions and stacking fault-stacking fault interactions in 6H-SiC was presented. The electronic structures and the total energies of 6H-SiC single crystals that contain one, two, three and four stacking faults were studied. The possibility of local hexagonal to cubic polytypic transformations was discussed in light of the formation energy and quantum-well action.

The main purpose of this article is to determine the two-dimensional effective mass tensors of electrons confined in thin 3C wells in hexagonal SiC, which is a first step in the understanding of in-plane electron motion in the novel quantum structures. We have performed ab initio band structure calculations, based on the density functional theory in the local density approximation, for single and multiple stacking faults leading to thin 3C-like regions in 4H- and 6H-SiC and deduced electron effective masses for two-dimensional electron gases around the cubic inclusions. We have found that electrons confined in the thin 3C-like layers have clearly heavier effective masses than in the perfect bulk 3C-SiC single crystal.

First-principles calculations of twin boundaries in 3C-SiC, Si, and diamond are performed, based on the density-functional theory in the local density approximation. We have investigated the formation energies and electronic properties of isolated and interacting twin boundaries. It is found that in 3C-SiC, interacting twin boundaries which are separated by more than two Si-C bilayers are actually energetically more favorable, implying a relatively frequent appearance of these defects. The effect of the spontaneous polarization associated with the hexagonal symmetry around twin boundaries is also studied, and we have observed that the wave functions belonging to the conduction- and valence-band edge states in 3C-SiC tend to be localized almost exclusively on different sides of the faulted layers, while there is no such feature in Si or diamond.