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 u sed here to characterize optical and electrical properties under a wide ran ge of injection levels, 10(14)-10(18) cm(-3), in low-doped n-type 4H-SiC ep ilayers. Our results reveal valuable anisotropy of the band-band absorption at the photon cm energy about 0.2 eV above the indirect band gap. While th e absorption coefficient is found nearly independent of the injection level . The ambipolar carrier diffusion coefficient is measured by an FCA-detecte d transient grating. Carrier diffusion length, bulk lifetime and surface re combination velocity is also estimated. (C) 1999 Elsevier Science S.A. All rights reserved.