Thickness Dependence of the Ground-State Exciton Energy in WSe2

A theory developed for a thin anisotropic semiconductor, where the exciton is treated in the effective-mass approximation and where the effect of crystal surfaces is included by means of image-charge potentials, is applied to crystals of thickness less than 500 Å. The theory leads to an exciton ground-state energy which closely approaches an inverse-square-law dependence on thickness. By the use of estimates of the dielectric and reduced-exciton-mass components quantitative agreement with data on W${\mathrm{Se}}_2$ is obtained.