Polarized electrolyte-electroreflectance study of ReS2 and ReSe2 layered semiconductors

Polarization dependent electrolyte-electroreflectance (EER) measurements of ReS2 and ReSe2 layered crystals have been carried out in the energy range of 1.3 to 5.0 eV. The EER spectra of E parallel to b polarization exhibit d istinct band-edge excitonic and interband transition features from those of E perpendicular to b polarization. Analysing the polarization dependent EE R spectra, the structures of the excitonic and interband transitions of ReS 2 and ReSe2 with optical polarizations along the b-axis and perpendicular t o the b-axis are examined clearly and the energy positions are determined a ccurately. The mechanism of field-lattice interaction is proposed to accoun t for the in-plane anisotropy of the crystals. Based on the analysis of exp erimental results, a probable bandstructure scheme of ReX2 (X = S, Se) is c onstructed.