A theory of the electronic properties of calcium fluoride(111) and silicon(111) surfaces and the CaF[sub 2]/Si(111) interface

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7112333

Engle, W P

The author has used an empirical tight binding-Green's function (ETB-GF) method to investigate the surface and interface properties of crystalline solids. The method allows the study of a semi-infinite sample and calculation of the positions of the localized states, their strengths, and how they decay into the bulk. This ETB-GF method can be used to calculate densities of the bulk states at each layer along with the individual contributions of the various orbitals and how they are modified by the presence of the surface. This technique has been used to calculate the bulk and surface properties of silicon (111) and calcium fluoride (111) as well as the interface properties of these two materials. For silicon, the author has extended the existing empirical tight binding Hamiltonian of Chadi and Cohen (CC) by incorporating two additional second nearest neighbor (2nn) terms. This resulted in a much better agreement in the conduction band with the empirical pseudopotential method (EPM) calculation of Chelikowsky and Cohen including more accurate gaps at [Lambda], X, and L, with a slightly less accurate valence band structure. The calculation of the As-passivated Si (111) system shows that it produces an unoccupied surface state in the band gap and two resonance states inside the valence band in close agreement with those found in previous experimental studies. This calculation predicts the existence of another localized state in the conduction band which has remained experimentally undetected. The material parameters were determined for CaF[sub 2] and the local density of states (LDOS) calculated for bulk CaF[sub 2] and the ideal, unrelaxed, unreconstructed surface layer. Surface states are shown at the fluorine and calcium layers due to cleaving of the bonds at the surface. The interface properties were studied of CaF[sub 2]/Si (111) and the LDOS calculated at each side of the interface. The results show an interface state in the gap.

• Research Organization: Drexel Univ., Philadelphia, PA (United States)
• OSTI ID: 7112333
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360606 -- Other Materials-- Physical Properties-- (1992-)
664100* -- Theory of Electronic Structure of Atoms & Molecules-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM FLUORIDES
CALCIUM HALIDES
CHEMICAL BONDS
ELECTRONIC STRUCTURE
ELEMENTS
FLUORIDES
FLUORINE COMPOUNDS
FUNCTIONS
GREEN FUNCTION
HALIDES
HALOGEN COMPOUNDS
INTERFACES
SEMIMETALS
SILICON
SURFACE PROPERTIES