3.2 Electronic Band Structure

The structure of the conduction and the valence band, as well as the bandgap energy are fundamental for the electronic properties of a semiconductor material. Since the early work on the band structure of SiC [112,113], it has been clear that the band structures of different polytypes can be compared by examining the relations between their Brillouin zones. In Fig. 3.4 the first Brillouin zone (1BZ) of $\alpha$-SiC is displayed [114], with the symmetry points $\Gamma$, M, L, A, K and H. The hexagonal [0001] plane direction is parallel to the $\Gamma$A-line and is chosen as the k$_z$-axis. The complex band structure is always calculated for fixed K $_\parallel$, along a path parallel to the k$_z$-axis.

Figure 3.4: First Brillouin zone of hexagonal Bravais lattice for $\alpha$-SiC.

By calculating the $\alpha$-SiC band structure along a variety of parallel directions one is able to find those points $K=K_\parallel+\Delta k_z$ at which the valence bands have their energy maximum and the conduction bands their energy minimum. The top of the valence band for 4H-SiC, as in fact for all other polytypes, is located at the $\Gamma$-point and the minimum of the conduction band at the M-point of the 1BZ, whereas the 6H-SiC has a camel's back structure for the lowest band along the ML-axis in the 1BZ [115].
T. Ayalew: SiC Semiconductor Devices Technology, Modeling, and Simulation