Isomer Shift and the Local Chemical Bond in Semiconductors

Abstract

In spite of many successful applications, some basic aspects of ion implantation, e.g. the local chemical bond of implanted atoms, their influence on the physical properties of the host crystal, etc., are still far from understood. This is mainly due to the presence of many defects or highly disordered regions in implanted materials which make it very difficult or impossible to apply sophisticated experimental methods used with perfect crystals. Also the theoretical description of implanted semiconductors is rather difficult since we are faced with the same or similar problems we encounter in amorphous materials. There is no doubt that experimental measurements on implanted materials giving new results together with the study of annealing processes are very desirable. In the past ten or so years the measurements of the Mossbauer isomer shift have proved to be of great value for more detailed studying of the electron structure of implanted semiconductors on atomic scale. It turns out in this connection that the occupancy numbers of the valence shells of atoms (ions), characterizing the local chemical bond, make it possible to interpret the isomer shift of the Mossbauer nucleus implanted in semiconducting material, and to understand its effect on the host crystal.