Application of EELS for Monitoring Defects Formed upon Ion-Implantation into Solid Matter
Thomas HOECHE 1, Frank Schrempel 2, Werner Wesch 2, Hans-Joachim Kleebe 3
e-mail: Hoeche@web.de
1 Chair of Crystallography, Institute of Physics, Humboldt University of Berlin,Invalidenstrasse 110, D - 10115 Berlin, Germany
2 Friedrich Schiller University Jena, Institute for Solid State Physics, Max-Wien-Platz 1, D - 07743 Jena, Germany
3 Colorado School of Mines, Metallurgical and Materials Engineering Department, Golden, CO 80401, USA
Crystalline substrates can be superficially modified by implanting ions into it. This method can be applied to either dope substrates in a controlled way or generate buried defects slightly below the surface. The latter effect is technologically relevant since amorphised slabs are used to border optical waveguide structures. Defect agglomerates can be used to trap impurities in semiconducting materials.
Apart from spatially resolved positron-annihilation spectroscopy, there is a severe lack in direct experimental techniques capable of monitoring the depth dependence of point defects generated by ion implantation. In particular, imaging and diffraction techniques in the transmission electron microscope are not sensitive to zero-dimensional defects.
We report on the application of dedicated analysis procedures to EELS depth scans recorded at Li+-implanted KTiOPO4 (KTP). It will be shown that the distribution of point defects does significantly effect the electronic structure which in turn manifests itself in particular features of the EEL spectrum. In particular, the depth distribution of oxygen vacancies in Li+:KTP can be determined by careful analysis of the pre-edge shoulder preceding the O K core-loss ionization edge.
Our EELS investigation is escorted by Rutherford backscattering spectroscopy, infrared refection spectroscopy, optical M-line spectroscopy, and measurements of the optical transmission.
Currently, we are extending the methodology to point defect distributions in He+-implanted LiNbO3 and self-implanted silicon.