Growth and characterization of Si1-x Mnx alloys on Si(100)

Si1-x Mnx alloy films of 50 nm thickness with 0.005≤x≤0.035 were grown by low-temperature molecular-beam epitaxy onto Si(100) substrates held at temperatures T in the range of 150 °C≤T≤350 °C. All films exhibit surface roughness with ∼20-nm -lateral and ∼1-nm -vertical length scales. This roughness is random for films with small x grown at the lower end of the temperature range. Films with larger x grown at higher T exhibit roughness organized into 〈110〉 -oriented cluster arrays centered on shallow surface depressions. This organized roughness correlates with the formation of subsurface complexes of four {111} planar defects or "funnel" defects. Mn-rich, nanometer-sized nodules form near the bottom of the Si1-x Mnx film and seed the formation of vertical, amorphous nanopipes. For growth of small x films at the lower end of the temperature range, these vertical nanopipes extend to the surface. In contrast, films with larger x grown at higher T form funnel defects which appear to emanate from the vertical nanopipes. Regardless of growth conditions, the Mn-rich nodules appear crystalline and do not correlate to any known Si-Mn phase. Ion channeling indicates that up to 90% of the Mn is substitutionally incorporated for samples with x=0.005. Although the substitutional fraction decreases with increasing x, the substitutional content increases. Our results indicate that Mn may be substitutionally incorporated in epitaxial thin films at concentrations of several orders of magnitude greater than its equilibrium solubility.