Temperature dependent study of the band edge excitons of ReS2 and ReSe2

ReS2 and ReSe2 are diamagnetic indirect semiconductors and belong to the family of transition-metal dichalcogenides crystallizing in the distorted octahedral layer structure of triclinic symmetry. We have measured the temperature dependence of the spectral features in the vicinity of the direct gaps E-g(d) in the temperature range between 25 and 525 K using piezoreflectance (PzR). The polarization dependence of the PzR spectra provides conclusive evidence that the features are associated with the interband excitonic transitions from different origins. From a detailed lineshape fit to the PzR spectra, we have been able to determine accurately the temperature dependence of the energies and broadening parameters of the band-edge excitons. The parameters that describe the temperature variation of the transition energies and broadening function have been evaluated and discussed. (C) 1997 Elsevier Science S.A.