Band edge absorption, carrier recombination and transport measurements in 4H-SiC epilayers

A depth-resolved technique based on probe-pump free carrier absorption (FCA) is especially useful for measurements in thin layers. This technique is used here to characterize optical and electrical properties under a wide range of injection levels, 1014–1018 cm−3, in low-doped n-type 4H-SiC epilayers. Our results reveal valuable anisotropy of the band-band absorption at the photon energy about 0.2 eV above the indirect band gap. While the absorption coefficient is found nearly independent of the injection level. The ambipolar carrier diffusion coefficient is measured by an FCA-detected transient grating. Carrier diffusion length, bulk lifetime and surface recombination velocity is also estimated.