Free Carrier Absorption in N-Type 6H-SiC

ABSTRACTFree carrier absorption (FCA) in n-type 6H-SiC doped with nitrogen has been studied in the energy range 50–250 cm-1 using samples of different free carrier concentrations ranging from 2.0–1016cm-3 to 7.0–1017cm-3. The index of wave number dependence of FCA p varies between -1.4 and -0.55 depending on free carrier concentration and electron mobility. The experimental results are in good agreement with the classical expression for the FCA coefficient. Quantum mechanical expressions for the FCA coefficient do not reproduce the measured p values. It is supposed that this is due to fact that the requirement for the application of perturbation theory ΩT ≫ 1 is not fulfilled. We investigated the anisotropy of FCA with respect to the c-axis and find a strong difference between ∝ ┴ and ∝∥.