Academic Verlag GMBH, Physica Status Solidi a Applied Research, 2(191), p. 613-620, 2002
DOI: 10.1002/1521-396x(200206)191:2<613::aid-pssa613>3.0.co;2-t
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We report on the absorption coefficient at 355 nm laser wavelength for 4H- and 6H-SiC over a wide temperature range. The measurements were carried out using a depth- and time-resolved free-carrier-absorption technique. The values of the absorption coefficient for the fundamental E ⊥ ĉ and E ∥ ĉ light polarization were extracted from the instantaneous profiles of the excess carrier concentration. The absorption dependency in 4H epilayers is consistent with a model based on the indirect optical transitions and shift of the energy gap with temperature. A discrepancy in absorption observed in heavily-doped 4H-SiC substrates at elevated temperatures is associated with a doping-induced narrowing of the band gap.