3.4.1 Dielectric Permittivity

No value for the relative dielectric constant of 4H-SiC seems to be published. However, the low frequency values measured by Patrick and Choyke [141] published in 1970 for the two tensor components of the static dielectric constant of 6H-SiC may be used for both polytypes. They found values of

$$\frac{\varepsilon_\perp}{\varepsilon_\parallel }=0.96,\hspace{0.5... ...=9.66,\hspace{0.5cm} \mathrm{and}\hspace{0.5cm}\varepsilon _{\parallel }=10.03.$$ (3.95)

In a more recent investigation, Ninomiya and Adachi [142] measured the dielectric permittivity of 6H-SiC perpendicular and parallel to the c-axis using spectroscopic ellipsometry. The measurement were conducted at room temperature on the [0001] plane of 6H-SiC with the photon energy range between 1.2 and 5.4 eV. They obtained the high-frequency dielectric constants as

$$\frac{\varepsilon_\perp}{\varepsilon_\parallel }=0.988,\hspace{0.... ...}=6.59,\hspace{0.5cm} \mathrm{and}\hspace{0.5cm}\varepsilon _{\parallel }=6.67,$$ (3.96)

and the static dielectric constants as

$$\frac{\varepsilon_\perp}{\varepsilon_\parallel }=0.978,\hspace{0.... ...}=9.76,\hspace{0.5cm} \mathrm{and}\hspace{0.5cm}\varepsilon _{\parallel }=9.98.$$ (3.97)

Since 4H-SiC has larger bandgap than 6H-SiC, one may expect the dielectric constants of this polytype to be somewhat smaller [23]. Additionally, the ratio of anisotropy may differ as the anisotropy of 4H-SiC seems to be generally weaker. T. Ayalew: SiC Semiconductor Devices Technology, Modeling, and Simulation