Temperature dependences of energies and broadening parameters of the band-edge excitons of Re-doped WS2 and 2H-WS2 single crystals

The temperature dependences of the spectral features in the vicinity of direct band-edge excitonic transitions for rhenium-doped (Re-doped) and undoped WS2 single crystals are measured over a temperature range of 15-300 K using piezoreflectance (PzR). From a detailed line shape fit of the PzR spectra, the temperature dependences of the energies and broadening parameters of the A and B excitons are determined accurately. The A and B excitonic transition energies show a red shift and a reduction of their splitting due to the presence of a small amount of Re and the broadening parameter of the excitonic transition features increases due to impurity scattering. The broader line width and the nature of the two-dimensional Mott-Wannier excitons of the 3R polytype prevent the detection of higher Rydberg series for the Re-doped samples. The parameters that describe the temperature variations of the energies and broadening functions of the excitonic transitions are evaluated and discussed.