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 cm(2)/s to an ambipolar diffusivity D-a = 4.2 cm(2)/s at approximately 10(16) cm(-3) with a substantial decrease occurring at higher injections. The derived D-h value corresponded to a minority-hole drift mobility of mu (h) = 90 cm(2)/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 similar to T-1.3 which notably differed from the expected one using the majority-hole mobility temperature dependence.