Chemical Interactions Among Defects in Germanium and Silicon

The effort of Wagner1 and his school to bring defects in solids into the domain of chemical reactants has provided a framework within which various abstruse statistical phenomena can be viewed in terms of the intuitive principle of mass action.2 Most of the work to date in this field has been performed on oxide and sulfide semiconductors or on ionic compounds such as silver chloride. In these materials the control of defects (impurities are to be regarded as defects) is not all that might be desired, and so with a few exceptions, experiments have been either semiquantitative or even qualitative. With the emergence of widespread interest in semi-conductors, culminating in the perfection of the transistor, quantities of extremely pure single crystal germanium and silicon have become available. In addition the physical properties, and even the quantum mechanical theory of the behavior of these substances have been widely investigated, so that a great deal of information concerning them exists. Coupled with the fact that defects in them, especially impurities, are particularly susceptible to control, these circumstances render germanium and silicon ideal substances in which to test many of the concepts associated with defect interactions. This view was adopted at Bell Telephone Laboratories a few years ago when experimental work was first undertaken. Not only has it been possible to demonstrate quantitatively the validity of the mass action principle applied to defects, but new kinds of interactions have been discovered and studied.