Non-destructive quantitative analysis of the Ge concentration in SiGe quantum wells by means of low energy RBS

The Ge concentration in MBE-grown SiGe quantum wells was quantitatively and non-destructively analyzed by means of low energy Rutherford backscattering (RBS). The Si1-x1Gex1 quantum wells were clad between Si1-x2Gex2 potential barriers, where x2 > x1. The thicknesses of the analyzed quantum wells were about 12 nm and they were situated at a depth of about 60 nm below the surface. Due to the lower Ge concentration in the quantum well a dip showed up in the RBS spectra, which was evaluated. In order to obtain quantitative results, a sufficiently good depth resolution is required, which was obtained by choosing a primary energy of 500 keV and a tilt angle between 45° and 51° with respect to the surface normal. From the raw data quantitative information was deduced by comparison with simulated spectra. To obtain a spectrum, a fluence of only 1 × 1013 projectiles/cm2 was needed, which makes the analysis virtually non-destructive. The Ge concentration in the quantum well could be determined with a precision of 1% absolute.