Modulation Spectroscopy on MoS2, and MoSe2

On MoS2 and MoSe2 crystals electroreflectance, piezoreflectance, thermoreflectance, and wavelength modulated reflectance is measured. From the evaluation of the spectra and from the comparison with bandstructure calculations it is most likely that the first direct transition is at point P of the Brillouin‐zone between bands formed by the non‐bonding states of the Mo atom. The four excitons near the fundamental edge correspond to this transition split by spin‐orbit coupling and by interlayer interaction. From electroreflectance above the absorption edge it is concluded that the valence bands of MoS2 correlated to the covalent bonds are less than 700 meV below the first occupied bands.