Trigonal manganese cluster in silicon: An electron-paramagnetic-resonance study

Besides the known tetrahedral ${\mathrm{Mn}}_{4}^{0}$ cluster, a second Mn cluster is observed by electron paramagnetic resonance in high-resistivity silicon doped with manganese. The spectrum shows trigonal symmetry. The analysis of the fine structure and the hyperfine structure suggests that the spectrum is due to a cluster consisting of four Mn ions forming a tetrahedron, [${\mathrm{Mn}}_{3\mathit{i}}^{0}$-${\mathrm{Mn}}_{\mathit{i}}^{\mathit{x}}$], where the fourth ${\mathrm{Mn}}^{\mathit{x}}$ ion gives rise to the trigonal symmetry. Most likely it is either a ${\mathrm{Mn}}^{\mathrm{\ensuremath{-}}}$ ion at an interstitial site or a ${\mathrm{Mn}}^{+}$ ion at a substitutional site. The [${\mathrm{Mn}}_{3\mathit{i}}^{0}$-${\mathrm{Mn}}_{\mathit{i}}^{\mathrm{\ensuremath{-}}}$] cluster model is favored. The observed S=11/2 ground-state manifold is the result of the dominant exchange coupling between the electronic spins of the four Mn constituents. The coordination of four ions in a tetrahedron seems to be an energetically preferred state during the formation of bigger clusters in the silicon lattice.

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