“…For the determination of the FCA coefficient ␣ FC ͑ , n͒, we have measured transmittance spectra at room temperature and at 77 K. In contrast to the reflectance spectra, the absorption coefficient is essentially determined by the imaginary part of the DF ⑀, i.e., Im͕⑀͖, which depends on the dominant scattering mechanism of the free carriers. For scattering of free carriers on acoustical (ac) and longitudinal optical phonons (op) as well as ionized impurities (imp), the following relation is approximately valid in the high-frequency limit, 4,5 i.e., ប Ͼ E F , where E F denotes the Fermi energy of the free carriers, and / ␥ ӷ 1…”