Optical Anisotropy of Transition Metal Dichalcogenides. A Photoelectrochemical Determination

Photoelectrochemical quantum efficiency measurements with polarized light incident at either (1010) or (0001) faces of VIb‐VIa compound semiconductors can be a successful probing technique for the absorption anisotropy. A condition is that the diffusion length of minority carriers towards the crystal faces being in contact with electrolyte is smaller than the reciprocal absorption coefficient, and the real parts of the refractive indices are known. It is found that the observed absorptivity ratios x / a z of MoS 2 , MoSe 2 , and WSe 2 attain unity near the indirect absorption edge, but gradually become considerably greater than unity for wavelengths approaching the direct transition.