The Antisymmetric Gap and the Total Width of the Valence Band of Binary Compound Crystals

Abstract

Soft X‐ray emission, X‐ray photoemission, and ultraviolet photoemission measurements of binary compounds show an antisymmetric gap within the valence band. The ratio of this antisymmetric gap to the total width of the valence band is shown to be a simple function of the Phillips‐van Vechten ionicity parameter of the compound. This relation is valid as well for tetrahedrally as for octahedrally coordinated compounds and for such elemental compounds (Se, Te) which contain two kinds of bonds. The relation is useful to determine the ionicity parameter of a compound and to test empirical band structure calculations which are fitted t o optical transition energies. Furthermore, also a relation for the estimation of the total valence band width in terms of the Fermi energy and the Penn gap is given.