Bonding and doping of simple icosahedral-boride semiconductors

A simple model of the bonding and doping of a series of icosahedral-boride insulators is presented. Icosahedral borides contain clusters of boron atoms that occupy the 12 vertices of icosahedra. This particular series of icosahedral borides share both the stoichiometry B12X2, where X denotes a group V element (P or As), and a conamon lattice structure. The inter-icosaliedral bonding of these icosahedral borides is contrasted with that of B12O2 and with that of alpha-rhombohedral boron. Knowledge of the various types of inter-icosahedral bonding is used as a basis to address effects of inter-icosahedral atomic substitutions. The intericosahedral bonding is maintained when an atom Of a group V element is replaced with an atom of a group IV element, thereby producing a p-type dopant. However, changes of inter-icosahedral bonding occur upon replacing an atom of a group V element with an atom of a group VI element or with a vacancy. As a result, these substitutions do not produce effective n-type dopants. Moreover, partial substitution of boron atoms for atoms of group V elements generally renders these materials p-type semiconductors. (C) 2003 Elsevier Inc. All rights reserved.