Transmission spectra of thin CdS and CdSe crystals near higher-order isotropic points |
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Authors: | G Czajkowski P Schillak |
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Institution: | (1) Scuola Normale Superiore, Pisa, Italia;(2) Academy of Technology and Agriculture, Bydgoszcz, Poland;(3) Present address: Department of Physics II, Academy of Technology and Agriculture, Kaliskiego 7, PL 85-790 Bydgoszcz, Poland |
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Abstract: | Summary For photon energies below the absorption edge in CdS, CdSe and other II–VI crystals the polariton dispersion curves forE⊥c andE‖c (c-axis in a wurtzite crystal) corss at some points called isotropic points (IP). The occurrence of isotropic points provides
the possibility of mode coupling between ordinary and extraordinary waves. Since the consequences of mode coupling on the
optical properties for photon energies near the lowest IP lying much below the first excitonic state were widely discussed
in recent years, more attention is now paid to isotropic points lying near the band gap and related to then=2,3, … excitonic states (?higher isotropic points?). Making use of Stahl's real density matrix approach we derive the polariton
dispersion relationsk
⊥ (ω), andk
‖ (ω), for CdS and CdSe bulk crystals and determine the positions of IP's due to the crossing of theB-polariton with higherA-excitonic resonances. By the method of multiple internal reflection we calculate the transmission spectra for various crystal
thicknesses (between 3 μm and 0.5 mm) and coupling mechanisms. The calculated transmission shows sharply peaked structures
centred at the isotropic points. |
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Keywords: | Excitons and related phenomena (including electron-hole drops) |
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