Emission Channeling Studies on the Behaviour of Light Alkali Atoms in Wide-Band-Gap Semiconductors

% IS342 \\ \\ A major problem in the development of electronic devices based on diamond and wide-band-gap II-VI compound semiconductors, like ZnSe, is the extreme difficulty of either n- or p-type doping. The only reports of successful n-type doping of diamond involves ion implanted Li, which was found to be an intersititial donor. Recent theoretical calculations suggest that Na, P and N dopant atoms are also good candidates for n-type doping of diamond. No experimental evidence has been obtained up to now, mainly because of the complex and partly unresolved defect situation created during ion implantation, which is necessary to incorporate potential donor atoms into diamond. \\ \\In the case of ZnSe, considerable effort has been invested in trying to fabricate pn-junctions in order to make efficient, blue-light emitting diodes. However, it has proved to be very difficult to obtain p-type ZnSe, mainly because of electrical compensation related to background donor impurities. Li and Na are believed to be amphoteric, i.e. acting as donor or acceptor depending on their lattice site. Besides N, they are the only dopant atoms which met with any success in producing p-type ZnSe. \\ \\Experimental data on the lattice site distribution of Li and Na dopant atoms and their stability on different lattice sites as a function of material properties, such as stoichiometry, are needed to understand the resulting electrical properties. This is also the subject of recent theoretical work. \\ \\The lattice site occupation and the stability of impurity atoms on different lattice sites can be studied by the emission channeling technique, which was successfully applied for the investigation of Si and III-V semiconductors at ISOLDE during the past few years. Initial promising results from emission channeling studies have been already obtained for $^{8}$Li in natural diamond and in as-grown ZnSe. \\ \\We propose to study the lattice site occupation of ion implanted $^{8}$Li and Na isotopes, such as $^{20}$Na, $^{21}$Na and $^{24}$Na, in natural and synthetic diamond as well as in ZnSe using the emission channeling technique. Our aim is to derive information on impurity lattice site distribution, the stability of interstitial impurities, the interaction with vacancy defects created during ion implantation, and the stability of substitutional impurity atoms. We request 15 shifts for $^{8}$Li and 15 shifts for Na isotopes