Anisotropic Thermal Conductivity of 4H and 6H Silicon Carbide Measured Using Time-Domain Thermoreflectance

Silicon carbide (SiC) is a wide bandgap (WBG) semiconductor with promising applications in high-power and high-frequency electronics. Among its many useful properties, the high thermal conductivity is crucial. In this letter, the anisotropic thermal conductivity of three SiC samples: n-type 4H-SiC (N-doped 1x10^19 cm-3), unintentionally doped (UID) semi-insulating (SI) 4H-SiC, and SI 6H-SiC (V-doped 1x10^17 cm-3), is measured using femtosecond laser based time-domain thermoreflectance (TDTR) over a temperature range from 250 K to 450 K. We simultaneously measure the thermal conductivity parallel to (k_r) and across the hexagonal plane (k_z) for SiC by choosing the appropriate laser spot radius and the modulation frequency for the TDTR measurements. For both k_r and k_z, the following decreasing order of thermal conductivity value is observed: SI 4H-SiC > n-type 4H-SiC > SI 6H-SiC. This work serves as an important benchmark for understanding thermal transport in WBG semiconductors.