Carrier diffusion characterization in epitaxial 4H–SiC

Carrier diffusivity has been experimentally determined in low-doped n-type epitaxial 4H–SiC over a wide injection range using a Fourier transient grating technique. The data showed that, with injection, the diffusion coefficient increased from a minority-hole diffusivity D_h = 2.3 cm²/s to an ambipolar diffusivity D_a = 4.2 cm²/s at approximately 10¹⁶ cm⁻³ with a substantial decrease occurring at higher injections. The derived D_h value corresponded to a minority-hole drift mobility of μ_h = 90 cm²/Vs, about 30% lower than available majority-hole mobilities. Also, the temperature dependence of the ambipolar diffusivity in the 296–523 K range has been determined. It followed a power law D_a ∼ T^−1.3 which notably differed from the expected one using the majority-hole mobility temperature dependence.