Density-Functional Theory Study of Half-Metallic Heterostructures: Interstitial Mn in Si

Using density-functional theory within the generalized gradient approximation, we show that Si-based heterostructures with $1/4$ layer $\delta$ doping of interstitial Mn (${\mathrm{Mn}}_{\mathrm{int}}$) are half-metallic. For ${\mathrm{Mn}}_{\mathrm{int}}$ concentrations of $1/2$ or 1 layer, the states induced in the band gap of $\delta$-doped heterostructures still display high spin polarization, about 85% and 60%, respectively. The proposed heterostructures are more stable than previously assumed $\delta$ layers of substitutional Mn. Contrary to widespread belief, the present study demonstrates that interstitial Mn can be utilized to tune the magnetic properties of Si, and thus provides a new clue for Si-based spintronics materials.

Figure 1

(a) (001)-$xy$-plane view and (b) (110)-$xz$-plane view of the Si-based heterostructure (modeled by a 16-layer supercell) with $1/4$ layer of interstitial Mn in $c(4\times 2)$ arrangement; (c) (001)-plane view of the heterostructure with $1/2$ layer of interstitial Mn in $p(2\times 2)$ arrangement; (d) (001)-plane view and (e) (110)-plane view of the heterostructure with a full layer of interstitial Mn in $(1\times 1)$ arrangement; (f) (001)-plane view and (g) (110)-plane view of the heterostructure with a full layer of substitutional Mn in $(1\times 1)$ arrangement. Black circles show Mn and gray circles Si atoms. The silicon atoms in different layers are marked with indices.

Figure 2

DOS of (a) the $1/4$-layer interstitial Mn $c(4\times 2)$, (b) the $1/2$-layer Mn $p(2\times 2)$, and (c) the 1-layer Mn $(1\times 1)$ heterostructures [cf. Figs. 1a, 1b, 1c, 1d, 1e]. The solid red (dashed blue) line refers to the down (up) spin component. The Fermi level is set to zero. (a) shows half-metallicity, (b) and (c) a high spin polarization at the Fermi level.

Figure 3

DOS of the 1-layer substitutional Mn. (a) $(1\times 1)$ heterostructure shows half-metallicity; (b) $p(2\times 2)$ heterostructure with extra $1/4$-layer coplanar interstitial Si shows, after an energetically favorable Si-Mn site interchange, the loss of half-metallicity. The solid red (dashed blue) line refers to the down (up) spin component.

Figure 4

Schematic view of the electronic states of the (a) interstitial and (b) substitutional Mn in Si [22]. The filled, patterned, and open circles indicate full, partial, and zero occupation, respectively. Both the size of the circles and the numbers next to the levels indicate their occupation number. The half-metallic DOS results in (a) from the $t_{2\downarrow }$ band, but in (b) from the $t_{2\uparrow }$ antibonding band.