D − shallow donor near a semiconductor–metal and a semiconductor–dielectric interface

Abstract

The ground state energy and the extent of the wavefunction of a negatively charged donor (D − ) located near a semiconductor–metal or a semiconductor–dielectric interfaceare obtained. We apply the effective mass approximation and use a variationaltwo-electron wavefunction that takes into account the influence of all image chargesthat arise due to the presence of the interface, as well as the correlation betweenthe two electrons bound to the donor. For a semiconductor–metal interface, theD − binding energy is enhanced for donor positionsd > 1.5aB (aB is the effective Bohr radius) due to the additional attraction of theelectrons with their images. When the donor approaches the interface (i.e. d < 1.5aB) theD − binding energy drops and eventually it becomes unbound. For asemiconductor–dielectric (or a semiconductor–vacuum) interface theD − binding energy is reduced for any donor position as compared to the bulk case andthe system becomes rapidly unbound when the donor approaches the interface.