Contains reports on two research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104)U.S. Navy - Office of Naval Research (Contract N00014-77-C-0132

Joannopoulos, John D.

Kunoff, Estelle M.

Lee, Dong-Hai T.

Wang, Yi-Ming

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III. SEMICONDUCTOR SURFACE STUDIESAcademic and Research StaffProf. J.D. JoannopoulosDr. J. IhmDr. Y-M. WangGraduate StudentsE.M. KunoffD-H. T. Lee1. EXCITATIONS AT SURFACES AND INTERFACES OF SOLIDSJoint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)John D. Joannopoulos, Yi-Ming Wang, Dong-Hai T. LeeWe are continuing our studies of the elementary excitations at surfaces andinterfaces of semiconducting systems. In particular, we have recently developeda successful theory of surface core-excitons that explains the unusual bindingenergies measured experimentally. Moreover, a universal limit to the bindingenergy is predicted that depends only on the nature of the atoms surrounding theexcitonic atom.We are also engaged in an investigation of the properties of compound wurtzitesurfaces. This includes a study of both the unique dimerlike and chainlike non-polar surfaces. Preliminary results on ZnO indicate important differences in thenature of the empty surface states at these surfaces. In addition, bona fidesurface states are predicted to exist in the d-like valence states of thismaterial.2. SURFACE AND DEFECT EXCITATIONS IN COVALENTLY BONDED SOLIDSU.S. Navy - Office of Naval Research (Contract N00014-77-C-0132)John D. Joannopoulos, Estelle M. KunoffA theory of the Si-Si0 2 interface based on recent experimental findings forsilicon surfaces and their oxidation has been developed. We find that a simplelocal-orbital picture can simultaneously describe silicon, its oxidation, and thePR No. 123(III. SEMICONDUCTOR SURFACE STUDIES)Si-Si0 2 interface. Calculations have been performed which show that interfacestates do not arise simply from the presence of a boundary. We find that bandtailing at the interface is due primarily to strain rather than to charged centers,and predict that dangling bands at the interface should give rise to an inhomo-geneously broadened discrete level at midgap.PR No. 123

Semiconductor Surface Studies

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Semiconductor Surface Studies

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