Polarized electrolyte-electroreflectance study of ReS2and ReSe2layered semiconductors

Polarization dependent electrolyte-electroreflectance (EER) measurements of ReS 2 and ReSe 2 layered crystals have been carried out in the energy range of 1.3 to 5.0 eV. The EER spectra of E ∥ b polarization exhibit distinct band-edge excitonic and interband transition features from those of E ⊥ b polarization. Analysing the polarization dependent EER spectra, the structures of the excitonic and interband transitions of ReS 2 and ReSe 2 with optical polarizations along the b -axis and perpendicular to the b -axis are examined clearly and the energy positions are determined accurately. The mechanism of field-lattice interaction is proposed to account for the in-plane anisotropy of the crystals. Based on the analysis of experimental results, a probable band-structure scheme of ReX 2 (X = S, Se) is constructed.