Cascade mixing in AlxGa1-xAs/GaAs during sputter profiling by noble-gas ions

The effect of cascade mixing on profile broadening during secondary-ion mas s spectrometry (SIMS) analysis has been thoroughly investigated for AlxGa1- xAs/GaAs structures of five different compositions (x = 0.1, 0.3, 0.5, 0.73 , or 1) and layers with varying thicknesses (from one monolayer to 1000 Ang strom). The SIMS analyses were performed using primary sputtering ions of N e-20(+), Ar-40(+), Kr-84(+), and Xe-136(+) with an impact energy (E) rangin g from 1.8 to 13.2 keV and an angle of incidence, with respect to the surfa ce normal (theta), from 620 to 35 degrees. Within the experimental accuracy , the decay length of the trailing edge was found to be proportional to E-1 /2 cos theta where the proportionality constant displays a relatively weak dependence on primary ion mass. However, the leading edge is strongly affec ted by the extension of the collision cascade as demonstrated by a comparis on of the results for the different ions at a given energy. As long as the cascade is fully developed before reaching an interface no dependence on th e sample depth is obtained for the profile broadening. Furthermore, the dec ay length for the trailing edges is extracted in the dilute limit and no ef fect of the marker thickness or the x value is revealed. A numerical treatm ent of the profile broadening within a diffusional model, where the diffusi on coefficient is assumed to be proportional to the energy deposited in ela stic collisions, gives a surprisingly good agreement with the experimental data. [S0163-1829(99)08543-4].