The Surface Effect on the Reflectivity Spectrum Originating from a Large Radius Exciton

The present paper aims at revealing the nature of the dead layer proposed by Hopfield and thomas with a model of an image force. First the motion of a Wannier exciton under the force is investigated in the adiabatic approximation. An adiabatic potential and an internal wave function of the lowest state are obtained for the opposite two cases in regards to the lowest state are obtained for the opposite two cases in regards to the mass ratio of an electron to a hole. The stability of an exciton near the surface is also discussed. Next a field-coupled polarization equation is set up. It contains the repulsive potential due to the image force, and the contact effect of the exciton with the surface. This equation is solved numerically under the boundary condition given by Hopfield and Thomas, and reflectivity spectra are obtained. In conclusion the image force is sufficient to yield an interference effect in case of the small mass ratio.