Adsorption, segregation, and magnetization of a single Mn adatom on the GaAs(110) surface

Density functional calculations with a large unit cell have been conducted to investigate adsorption, segregation, and magnetization of Mn monomer on GaAs(110). The Mn adatom is rather mobile along the trench on GaAs(110) with an energy barrier of $0.56\mathrm{eV}$. The energy barrier for segregation across the trenches is nevertheless very high, $1.67\mathrm{eV}$. The plot of density of states display a wide gap in the majority spin channel, but show plenty of metal-induced gap states in the minority spin channel. The Mn atoms might be “invisible” in scanning tunneling microscope (STM) images taken with small biases, due to the directional p–d hybridization. For example, one will more likely see two bright spots on $\mathrm{Mn}∕\mathrm{Ga}\mathrm{As}\left(110\right)$, despite the fact there is only one Mn adatom in the system.

Figure 1

(Color online) A sketch of the $p(3\times 3)$ unit cell and adsorption configurations for the simulations of $\mathrm{Mn}∕\mathrm{Ga}\mathrm{As}\left(110\right)$. The dashed rectangle gives the primitive 2D unit cell for the clean GaAs(110) surface.

Figure 2

(Color online) The potential-energy surface for Mn diffusion on GaAs(110). Dark colors indicate higher binding energies whereas light colors represent lower binding energies. The balls and straight black lines give the position of the surface and subsurface Ga and As atoms and the bonds between them. The red (light gray) line shows the minimum energy segregation path and the inset gives the total energy versus the position of Mn along this path.

Figure 3

(Color online) The atom-projected density of states for Mn (green or light lines) and its nearest Ga (blue or dark lines) and As (red or gray lines) neighbors. Results in panels (a), (b), (c), and (d) are for the interstitial Mn in the bulk GaAs (at the $T_{\mathit{Ga}}$ site), Mn adatom on $T_{\mathit{Ga}}$, $T_{\mathit{As}}$ and hexagonal sites over GaAs(110), respectively. States in the majority and minority spins are separated with positive and negative signs. Zero energy in the horizontal axis indicates the position of the Fermi level.

Figure 4

(Color online) (a) The schematic energy and wave function diagrams of the gap states. (b) The energy-sliced charge densities plotted in a horizontal plane which is $4\mathrm{\AA }$ above the Mn adatom for the $T_{\mathit{Ga}}$ configurations. States only within $-0.25\mathrm{eV}\text{to}+0.25\mathrm{eV}$ around $E_F$ contribute to the plots.