O 2 + probe‐sample conditions for ultra low energy SIMS depth profiling of nanometre scale Si 0.4 Ge 0.6 /Ge quantum wells

The O 2 + probe‐sample conditions and subsequent data analysis required to obtain high depth resolution SIMS depth profiles from Si 1− x Ge x /Ge quantum well structures (0.6 ≤ x ≤ 1) are presented. For primary beam energies E p  >500 eV and x approaching 1, a significant decrease in the Ge + ionisation probability resulted in unrepresentative and unquantifiable depth profiles. For E p  ≤ 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 Si 1− x Ge x 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.