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RESEARCH PRODUCT
Excitonic absorption and Urbach's tail in bismuth sulfide single crystals
A. SeguraJuan P. Martínez-pastorAndrés CantareroA. Chevysubject
Physics and Astronomy (miscellaneous)business.industryChemistryBand gapExcitonGeneral EngineeringGeneral ChemistryMolecular physicsMolecular electronic transitionOpticsAbsorption edgeAttenuation coefficientAbsorptanceGeneral Materials SciencebusinessAbsorption (electromagnetic radiation)Single crystaldescription
The absorption coefficient of bismuth sulfide single crystals has been measured through more than four orders of magnitude and in the range of energies from 1.25 to 1.70 eV. A detailed study as a function of temperature has been carried out from 29 to 300 K. An Urbach tail for low values of absorption has been found. This tail and its temperature evolution fit the expression for ionic materials. An excitonic region appears at low temperature and the shape of the exciton peak is Gaussian, which corresponds to a strong exciton-phonon coupling. The exciton binding energy is estimated (28±3 meV) and then the energy gap at 29 K is obtained (Eg=1.523±0.003 eV). The fundamental electronic transition has been found to be a strongly anisotropic allowed direct transition. From reflectivity measurements a localized level at 1.361 eV at 29 K has been found. The change of the gap with temperature is interpreted through an electron-phonon mechanism.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 1988-08-01 | Applied Physics A: Solids and Surface |