 
Summary: Effects of interfacial charges on semiconductor films
A. M. Alencar, R. N. Costa Filho, V. N. Freire, and G. A. Farias
Departamento de Fi´sica, Universidade Federal do Ceara´, Campus do Pici, Centro de Cie^ncias Exatas, Caixa Postal 6030,
60455760 Fortaleza, Ceara´, Brazil
Received 18 November 1997
The electronphonon coupling and the confined electron binding energy in a semiconductor film with a
charge density at both surfaces is investigated. Maxwell equations are solved with appropriate boundary
conditions to calculate the dispersion relation of bulk longitudinaloptical LO and surfaceoptical SO
phonons. The Hamiltonian that describes the electronphonon interaction is obtained through a quantum treat
ment, and a perturbation theory up to the second order is used to calculate the groundstate energy of confined
polarons. Numerical results are obtained for the dispersion relation, the electronphonon coupling function, and
the groundstate energy of polarons in GaAs films. It is shown that the charged interfaces do not change the
volume modes of a GaAs film, but alter significantly its surface modes. The dispersion relation of SO phonons,
the electronphonon coupling function, and the groundstate energy of the polaron depend on the surface
charge density, as well as on the film thickness. S01631829 98 032196
I. INTRODUCTION
The interaction between electrons and elementary excita
tions in the neighborhood of a surface is a matter of rel
evance to the development of technological applications.
There has been great interest in the investigation of the prop
