Excitons in 2H-WSe₂and 3R-WS₂

Abstract

The A exciton series in the liquid-nitrogen-temperature epsilon 2 spectra of 2H-WSe2 and 3R-WS2, derived from Kramers-Kronig analyses of normal-incidence, basal-plane reflectivity spectra, have been fitted to a Lorentzian oscillator model. It has been found that the energy levels and oscillator strengths of the excitons obey a three-dimensional theoretical model for 2H-WSe2 and a two-dimensional model for 3R-WS2. The experimental observations are consistent with Toyozawa's (1958) theory for weak exciton-phonon interactions and small exciton effective mass.