Growth and characterization of Si1−xMnx alloys on Si(100)

Abstract

Si 1 − x Mn x 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−xMnx 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.

Ferromagnetism of MnxSi1-x(x ∼ 0.5) films grown in the shadow geometry by pulsed laser deposition method

“…17,18 No essential manifestations of HT FM caused by these nanocolumns were revealed in Refs. 17 and 18.…”

High-temperature ferromagnetism in Si:Mn alloys

“…In the ideal bulk MnSi 1.7 27 Si 47 revealed that these phases are half-metallic, with full spin polarization of the carriers (holes) at the Fermi level. On the contrary, the ideally stoichiometric and unstressed Mn 4 Si 7 silicide is shown to be a semiconductor, with indirect band gap, although small nonstoichiometry or stress lead to the closure of the gap, transforming the material into a metal.…”

“…Moreover, there is experimental evidence for the formation of vertical Mn-enriched nanopipes in Si 1−x Mn x alloys grown on a Si(100) substrate. 27 Also the inspection of the local environment of Mn in the Mn δ-doped Si samples prepared by MBE on Si(001) substrates did not exclude a precipitation. 28 We point out that, in the case of the layer, the averaging procedure to determine ϕ(r) consists in integrating over the Cartesian coordinates parallel to the layer (say, y and z).…”

Magnetic Semiconductors

“…Growth of polycrystalline Mn-doped Si with Mn composition more than 0.1 was carried out on Si (001) substrate at T S ¼ 300 C by using gas-source MBE [209]; it was, however, later shown that there is formation of Mn-rich precipitates during MBE growth even at T S ¼ 150 C [210]. Growth of polycrystalline Mn-doped Si with Mn composition more than 0.1 was carried out on Si (001) substrate at T S ¼ 300 C by using gas-source MBE [209]; it was, however, later shown that there is formation of Mn-rich precipitates during MBE growth even at T S ¼ 150 C [210].…”