Binding Energy of Excitons Bound to Neutral Donors in Two-Dimensional Semiconductors

The binding energies of excitons bound to neutral donors in two-dimensional(2D)semiconductors within the spherical-effective-mass approximation,which are nondegenerate energy bands,have been calculated by a variational method for a relevant range of the effective electron-to-hole mass ratio a.The ratio of the binding energy of a 2D exciton bound to a neutral donor to that of a 2D neutral donor is found to be from 0.58 to 0.10.In the limit of vanishing o and large a,the results agree fairly well with previous experimental results.The results of this approach are compared with those of earlier theories.