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We begin by considering the germanium semiconductor. The crystal of this element has the diamond structure As we have seen, this structure consists of two interpenetrating fcc lattices. A germanium atom at point B in the figure is bonded to four neighboring atoms. Germanium has one 4s wave function and three 4p wave functions which combine to form four hybrid wave functions directed to the corners of a tetrahedron centered at B. Hybrid orbitals of this kind are illustrated The covalent bond between neighboring germanium
atoms is due to the sharing of electron pairs in each of these bonding orbitals. we see that the atom at B has four nearest neighbors, arranged at the vertices of a tetrahedron. Each of these
atoms is also joined in a similar fashion to its neighbors. It is instructive to compare the crystal structure of Ge to that of InSb. While germanium is in column IV of the periodic table, indium (In) is in column III, and antimony (Sb) is in column V. The InSb
semiconductor forms the same diamond structure as germanium with indium
atoms occupying all of the A sites of the crystal and antimony
atoms occupying all of the B sites. A schematic representation of the InSb structure. The electronic structure of InSb is very similar to that of germanium. In each case, eight valence electrons are distributed among the four bonds. However, whereas the four electron pairs occur midway between the germanium
atoms in the germanium structure, the electron pairs are drawn more closely to the Sb atom in the InSb lattice. This can be explained with the concept of electronegativity used in modern chemistry.
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