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

The O₂⁺ 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. [ABSTRACT FROM AUTHOR]