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O2+ probe-sample conditions for ultra low energy SIMS depth profiling of nanometre scale Si0.4Ge0.6/Ge quantum wells


R. J. H. Morris, Physics Department, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.



The O2+ probe-sample conditions and subsequent data analysis required to obtain high depth resolution SIMS depth profiles from Si1−xGex/Ge quantum well structures (0.6 ≤ x ≤ 1) are presented. For primary beam energies Ep >500 eV and x approaching 1, a significant decrease in the Ge+ ionisation probability resulted in unrepresentative and unquantifiable depth profiles. For Ep ≤ 500 eV, a monotonic increase in the Ge+ signal with x was observed resulting in profiles representative of the sample structure and enabling x to be found. A depth scale was also established using a point-by-point approach taking into account the local erosion rate, which is a function of x. Both the composition and the thickness of the Si1−xGex and Ge layers were found to be in excellent agreement with those obtained using X-ray and transmission electron microscopy. Copyright © 2012 John Wiley & Sons, Ltd.