We have measured the temperature dependence of the spectral features in the vicinity of direct band-edge excitonic transitions of single crystals from 25 to 300 K using piezoreflectance (PzR). From a detailed lineshape fit of the PzR spectra, the energies and broadening parameters of the A and B excitons have been determined accurately. The origin of these excitonic transitions is discussed. The transition energies and their splittings vary smoothly with the tungsten composition x, indicating that the natures of the direct band edges are similar for the compounds. In addition, the parameters that describe the temperature variation of the energies and broadening function of the excitonic transitions are evaluated and discussed.

Polarization-dependent absorption measurements of ReS 2 and ReSe 2 single crystals have been carried out in the temperature range between 25 and 500 K. A significant shift towards lower energies has been observed in the transmittance spectra of Eʈb polarization with respect to those corresponding to EЌb polarization. Analysis reveals that the absorption edges of ReS 2 and ReSe 2 are indirect allowed transitions. The parameters that describe the temperature dependence of the absorption edges with different polarizations in the van der Waals plane are evaluated. The results indicate that the electron-phonon coupling constants for Eʈb polarization are considerably larger than those of EЌb polarization. ͓S0163-1829͑98͒02748-9͔ PRB 58 16 133 ABSORPTION-EDGE ANISOTROPY IN ReS 2 AND . . .

In-plane anisotropic optical and electrical properties of layered ReS2 crystals are reported. The optical anisotropic effects for E || b polarization and E b polarization were studied through polarization-dependent piezoreflectance and optical absorption measurements. The resistivity perpendicular to the b-axis was shown to be several times larger than that along the b-axis.

No abstract

No abstract