Lattice Location of Low-Z Impurities in Medium-Z Targets Using Ion-Induced X-Rays
The common method of Rutherford backscattering and channeling of light energetic ions is in general not suited to lattice location studies of impurity atoms having a mass similar to or lower than the host. While specific nuclear reactions are sometimes available they usually require high beam doses and yield high backgrounds of scattered particles. In two such situations we have used ion induced x-ray yields to determine lattice location viz. for 32S and 31P implants in Ge single crystals. In the course of this work we have had to identify and optimize a number of experimental parameters, in particular how the beam type affects (a) ψ1/2,xmin and crystal damage rates, (b) x-ray yields (P-K, S-K, Ge-L and Ge-K), target bremsstrahlung and recoil-induced molecular x-ray intensities. Choice of detector geometry, aperture and window also proved to be important. Detection limits for P and S are now certainly better than 1 x 1014 atoms.cm-2 in a thick Ge target for 0.5 MeV proton excitation. We have found that a room temperature implant of 40 keV 31P annealed at 450oC is highly (93%) substitutional in Ge for a dose of 0.7 x 1015 ions.cm-2, but shows a much lower fraction at 2.7 x 1015 ions.cm. Lattice location of S implanted into Ge parallels the pattern from Group VI impurities implanted and annealed in Si, showing ≤ 50% xmin. values for the S signals in <110> and <111> directions. A different distribution for S is implied by <100> channeling data and <111> and <110> angular scans.
KeywordsLattice Location Beam Type Angular Scan Substitutional Fraction Target Bremsstrahlung
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- See, for example, J. W. Mayer, L. Eriksson and J. A. Davies, “Ion Implantation in Semiconductors”, (Academic Press, New York, 1970).Google Scholar
- E. Merzbacher and H. W. Lewis, Handbuch der Physik, Vol. 34, (Ed. S. Flügge, Springer-Verlag, 1958) 166 ff.Google Scholar
- F. W. Saris, I. V. Mitchell and J. F. Chemin, to be published.Google Scholar
- K. B. Winterbon, “Range-Energy Data for keV Ions in Amorphous Materials”, AECL-3194 (1968).Google Scholar
- S. T. Picraux, N. G. E. Johansson and J. W. Mayer, in “Semiconductor Silicon” Ed. by R. R. Haberecht and E. L. Kern (Electrochemical Society, New York, 1969) p. 422.Google Scholar