Lattice Location of Transition Metals in Semiconductors

%IS366 %title\\ \\Transition metals (TMs) in semiconductors have been the subject of considerable research for nearly 40 years. This is due both to their role as important model impurities for deep centers in semiconductors, and to their technological impact as widespread contaminants in Si processing, where the miniaturization of devices requires to keep their sheet concentration below 10$^{10}$ cm$^{-2}$. As a consequence of the low TM solubility, conventional ion beam methods for direct lattice location have failed completely in identifying the lattice sites of isolated transition metals. Although electron paramagnetic resonance (EPR) has yielded valuable information on a variety of TM centers, it has been unable to detect certain defects considered by theory, e.g., isolated interstitial or substitutional Cu in Si. The proposed identity of other EPR centers such as substitutional Fe in Si, still needs confirmation by additional experimental methods. As a consequence, the knowledge on the structural properties of TM defects is insufficient.\\ \\We propose to study the lattice sites of the transition metals Fe, Cu and Ag in semiconductors by means of the electron emission channeling effect from radioactive probe atoms. This new experimental approach is made possible due to the recently developed laser ionization sources for transition metals at ISOLDE, and the realization of suitable position-sensitive electron detectors by CERN's Silicon Strip Detector group. We intend to implant radioactive Fe, Cu and Ag isotopes at room temperature, followed by a characterization of the as-implanted lattice sites. Measuring the emission channeling effect as a function of sample annealing temperature will then allow us to derive the thermal stability of the as-implanted sites, and possibly also to observe the formation of (TM-acceptor) complexes. The experiments should start with Si and be extended to other semiconductors later on.