Modulation Spectroscopy on the Group IV and VI Transition‐Metal Dichalcogenides

Piezoreflectance, thermoreflectance, and wavelength modulated reflectance are measured on the group IV and VI compounds of transition‐metal dichalcogenides. From the evaluation of the spectra by different modulation techniques, from the alloying effect which is first investigated, and from the comparison with the band structure calculations, it is most likely that the A and B excitons observed in the absorption edge of the group VI compounds correspond to the d—d transitions, while the A′ and B′ excitons observed in the higher‐energy side correspond to the p—d transitions. For the group IV compounds the modulated reflectance is first measured and new peaks are found. The comparison with the band structure calculations is also carried out.