Excitonic Polaritons and Electronic Band Structure of CdAl₂S₄ Single Crystals

摘要

Reflection and wavelength modulated reflection spectra were investigated at temperature 10 K in CdAl2S4 crystals. Ground and excited states of three excitonic series (A, B and C) were found out. Contours of excitonic reflection spectra were calculated and main parameters of excitons and bands in k = 0 were determined. The effective mass of electrons mc is equal to 0.30m0 and holes masses mv1, mv2 and mv3 are equal to 1.55m0, 0.90m0 and 2.07m0, respectively in Γ point of Brillouin zone. Valence bands V1 - V2 splitting due to crystal field (141 meV) and bands V2 - V3 splitting by spin-orbital interaction (152 meV) were estimated. Spectral dependences of optical functions (n, k, ε1 and ε2) were determined by Kramers-Kronig analysis of reflection spectra measured at energies 3 - 6 eV and in E?c and E||c polarizations. Energies of direct electron transitions were determined and identified in the actual points of Brillouin zone in the framework of actual band structure theoretical calculations of CdAl2S4.