Temperature dependences of energies and broadening parameters of the band-edge excitons of Re-doped WS₂and 2H-WS₂single crystals

Abstract

The temperature dependences of the spectral features in the vicinity of direct band-edge excitonic transitions for rhenium-doped (Re-doped) and undoped WS 2 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.

Temperature dependence anisotropic photoconductivity in 2H-MoSe2 single crystals

“…In our present case for the 2H-MoSe 2 single crystal, a reasonably good fit using the two models over the entire temperature range from near zero to room temperature of the experimentally observed variation of the anisotropic energy gap is demonstrated. It is suggested that temperature shift of the indirect energy gap is probably due to the interaction with relevant acoustic and optical phonons [22]. By comparing with the indirect gap anisotropy, we see that the mechanism of crystal anisotropy as a result of van der Waals interaction has an influence on the indirect gap and this finding concurred well with the study on other layered structure compounds such as MoS 2 [23] and WSe 2 [24].…”

Photoacoustic and modulated reflectance studies of indirect and direct band gap in van der Waals crystals

“…So far most of them (MoS 2 , MoSe 2 , WS 2 , WSe 2 , ReS 2 , and ReSe 2 ) were studied by MR (photoreflectance, electroreflectance or piezoreflectance) 12,39–41,43–46 , but none of them was studied by PA spectroscopy. In order to discuss chemical trends for the indirect and direct gap in these materials, they are grouped in a few sets of samples going from smaller to larger atoms.…”

Piezoreflectance study of near band edge excitonic-transitions of mixed-layered crystal Mo(SxSe1-x)2 solid solutions

“…The obtained values of C ex i (0), C iLO , and H iLO are listed in Table IV together with the numbers for MX 2 . 20,28,29 The value of C ex i (0) for A 1 (B) excitonic transitions of MoSe 2 and MoS 2 are 19 (36) and 20 (37) meV, respectively. The larger values of C ex i (0) for mixed ternary Mo(S x Se 1-x ) 2 crystals are larger than binary ones due mainly to the alloy scattering effects.…”