properties, which overcomes silicon materials for applications in high-power and high-

temperature electronics [16]. Compared to silicon, SiC has three times the thermal con­

ductivity, ten times the critical electric field strength, and three times the bandgap [16].

Additionally, SiC exhibits a short bond length of 1.89 Å for Si-C bond, which is 88%

covalent and 12% ionic [6]. These strong bonds give the SiC materials high chemical

inertness, hardness, thermal conductivity, and critical electric field strength, enabling

applications in extreme environments (see main properties at Section 13.3 – Table 13.1).

The stability and oxidation tolerance of SiC allows it to work at an elevated temperature

up to 600°C, being useful for applications in piezoresistive and thermoresistive sensors

and long-term implantation.

Silicon carbide has over 250 polytypes of crystalline structures that will change de­

pending on the stacking sequence of the tetrahedrally bonded Si-C bilayers [2]. Each Si-C

bilayer is composed of two coupled planar sheets, one of the silicon atoms and another of

carbon atoms, and this bilayer is the basal plane in direction of the c-axis. The SiC bilayer

planes can be stacked to form either a ZB (cubic) or WZ (hexagonal) crystal structures,

and they will have two polar planes referred to as Si-plane and C-plane. A common

polytype with cubic structure is the 3C-SiC, also known as β-SiC, and it will have a

stacking of three bilayer periodicities (Figure 13.3) [17]. The family of polytypes with WZ

(hexagonal) crystal structure is referred to as α-SiC, and it includes polytypes with purely

hexagonal structure or mixtures of cubic and hexagonal structures. The pure wurtzite

polytype is the 2H-SiC with a stacking periodicity of two bilayers [17]. The common

compounds 4H-SiC and 6H-SiC (Figure 13.3) have in their structure a portion of cubic

elements; however, the overall is hexagonal crystal symmetry. The 4H-SiC is composed of

an equal proportion of cubic and hexagonal bonds, while 6H-SiC for two-thirds of cubic

bonds, and each compound will have four and six bilayers stacking periodicity, respec­

tively [17]. Additionally, the silicon carbide can also form rhombohedral structures, the

15R- and 21R-SiC.

FIGURE 13.2

The different polar, nonpolar , and semipolar plane orientations.

Wide Bandgap Semiconductors

207