Fundamental band edge absorption in nominally undoped and doped 4H-SiC
2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 12Article in journal (Refereed) Published
Fundamental band edge absorption is investigated in nominally undoped (n < 1014 cm(-3)) and heavily doped (n similar to 8 x 10(18) cm(-3)) 4H-SiC by a spectroscopy technique based on spatially and time-resolved free-carrier absorption. The spectra are extracted over a wide absorption range (0.02-500 cm(-1)) at temperatures from 75 to 450 K. The experimental results are supported by an indirect transition theory with a unique set of dominating momentum-conserving phonons, showing good correlation with earlier findings of differential absorption measurements at 2 K. Exciton binding energy of 30 +/- 10 meV is derived from fitting the data at 75 K. The detected polarization anisotropy of absorption with respect to c axis is shown to be consistent with the selection rules for the corresponding phonon branches. An analytical model related to constant degree of involved phonons describes well the obtained energy gap variation with temperature. Finally, doping induced band gap narrowing is characterized above the impurity-Mott transition and compared with theoretical calculations in the random phase approximation. The shape of the fundamental absorption edge at high carrier concentrations is discussed in terms of excitonic enhancement above the Mott transition, as recently detected in Si.
Place, publisher, year, edition, pages
2007. Vol. 101, no 12
intrinsic optical-absorption, silicon-carbide polytypes, free-carrier-absorption, temperature-dependence, n-type, 4h, gap, si, semiconductors, recombination
IdentifiersURN: urn:nbn:se:kth:diva-16745DOI: 10.1063/1.2749335ISI: 000247625700047ScopusID: 2-s2.0-34547322966OAI: oai:DiVA.org:kth-16745DiVA: diva2:334788
QC 201005252010-08-052010-08-05Bibliographically approved