Structure and bonding in narrow gap semiconductors

Abstract

Many trends in the behavior of elements and their compounds are immediately visible by comparison with their position in the periodic table. The most obvious trend is that the elements to the left and in the lower part of the periodic table are metals while the rest are covalently-bonded semiconductors or insulators; the coordination number of the covalently-bonded materials is generally given by the 8-N rule (N is the column number). The next clear trend comes in the consideration of binary compounds; here we find that the horizontal separation of the two elements in the periodic table is a good indication of their ionicity. For example, this explains the trends in the forbidden energy gap and the crystal structure along an isoelectronic series (e.g. KBr, Case, ZnSe, GaAs, Ge).