The Dissociation Energy of the Surface Biexciton

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Abstract
The effective Hamiltonian of two electrons and two holes located near the boundary of the polar crystal and the vacuum, interacting via the Coulomb law and through exchange by virtual surface longitudinal optical phonons is derived. On ground of the approximate form of this Hamiltonian the binding energies Wm(σ) of the surface biexciton are estimated in the whole range of mass ratio 0 ≦ σ = me/mh ≦ 1 (me and mh is the effective mass of the electron and of the hole, respectively). The surface biexciton is stable at all σ and the dissociation energy is greater than that of bulk biexciton.