Determination of the polarization dependence of the free-carrier-absorption in 4H-SiC at high-level photoinjection

Strong polarization anisotropy of the free-carrier-absorption (FCA), induced by a pulsed pump beam, has been observed in low-doped 4H-SiC. The FCA cross-sections are determined at four energies for the electrical vector E being perpendicular and parallel to the c-axis. The connection to Biedermann's inter-conduction-band transitions is found by comparing the FCA cross-sections with those measured in the n-type heavily doped substrate. The energy dependencies of the FCA cross-section value also provide evidence for the existence of an additional FCA intraband optical transition for E perpendicular toc. An astonishing effect of the fractional absorption damping is identified in the FCA-transient at lower detected energies for the E parallel toc cases.