The optical energy gap in Mo0.5W0.5Se2 single crystals grown by a direct vapour transport technique

Optical absorption in single crystals of Mo0.5W0.5Se2 has been measured at room temperature near the fundamental absorption edge. The incident light was kept normal to the basal plane i.e. along the c-axis of the grown flakes. Results have been analyzed on the basis of two dimensional and three dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The direct and indirect energy gaps and phonon energies were found to be 1.56 eV, 1.02 eV and 10 MeV, 40 MeV respectively. The three dimensional model and not the two dimensional model could be used to describe the optical properties of Mo0.5W0.5Se2 single crystals. (author)