Medium energy ion scattering (MEIS) studies on Si/GaSb/Si- and Si/CaF2/Si(111) layer systems

The layer systems Si/GaSb/Si and Si/CaF2/Si(111) are fabricated by MBE. The thickness of the interlayers are about 1 monolayer and a few nm. The composition and geometric structure of the layer systems is studied with MEIS. The systems are well suited for MEIS-studies because both the GaSb and CaF2-signals in the MEIS spectra can be separated from the silicon background, CaF2 has almost the same lattice constant as silicon. It turns out that Si/CaF2/Si(111) can be grown epitaxially for an interlayer thickness of about 5 nm. This has been earlier found by other groups for layer systems with larger thicknesses. An attempt to produce corresponding systems with a CaF2 thickness of only 1 monolayer resulted in diffusion of CaF2 from the interface. The lattice constant of GaSb is about 12% larger than chat of silicon making epitaxial growth by far more difficult. Partly epitaxial GaSb-islands are observed for deposition at about 200 degrees C, In this case, the attempt to produce a system with GaSb thickness of only 1 monolayer by overgrowth of GaSb with silicon at 200 degrees C and heating the system to 600 degrees C yields an epitaxial silicon cap layer. GaSb remains at the interface, For the quantitative analysis of the MEIS data Monte Carlo calculations of the ion trajectories are performed for comparison with the experimental spectra. The simulations take into account all shadowing and blocking effects in the layer systems. The simulations show that MEIS is an excellent method to determine the orientation of GaSb-dipoles quantitatively.