Ab initio study of the interface properties of Fe/GaAs(110)

We have investigated the initial growth of Fe on GaAs(110) by means of density-functional theory. In contrast to the conventionally used (001) surface the (110) surface does not reconstruct. Therefore, a flat interface and small diffusion can be expected, which makes Fe/GaAs(110) a possible candidate for spintronic applications. Since experimentally, the actual quality of the interface seems to depend on the growth conditions, e.g., on the flux rate, we simulate the effect of different flux rates by different Fe coverages of the semiconductor surface. Systems with low coverages are highly diffusive. With increasing amount of Fe, i.e., higher flux rates, a flat interface becomes more stable. The magnetic structure strongly depends on the Fe coverage but no quenching of the magnetic moments is observed in our calculations.

Figure 1

(Color online) The relaxed free GaAs(110) surface. The bottom of the cell is passivated with pseudohydrogen, $\omega$ represents the relaxation angle between the surface atoms.

Figure 2

(Color online) Relaxed structure in case of 1/4 monolayer of Fe on the GaAs(110) surface, which is the energetically most favorable configuration 1, see also Fig. 3.

Figure 3

(Color online) Top: Top view of the relaxed GaAs(110) surface. The brighter ions mark the bulk positions of the corresponding atoms while the darker ions illustrate the relaxed position at the free surface. The different investigated Fe positions are indicated by the grid. Numbers label the 3 Fe positions which are most favorable. The triangles mark a metastable state, see text and ‘‘a’’ corresponds to the energetically most favorable configuration with interdiffusion. Bottom: The energy surface in eV for the Fe positions on the above shown grid. Contour lines are at a distance of 0.25 eV.

Figure 4

(Color online) Top: Relaxed supercell with a monolayer of Fe on the free GaAs(110) surface. Bottom: Relaxed supercell after a second monolayers of Fe has been placed on the supercell above. The bottom of the cell is passivated with pseudohydrogen.

Figure 5

(Color online) Top: Top view of the ideal Fe/GaAs interface in the most favorable configuration. Additionally, the Fe layer has been shifted rigidly relative to the GaAs surface as indicated by the white arrows. For each grid point the energy has been calculated. Bottom: Energy surface of the ideal Fe/GaAs system for the different configurations defined above. The energy is given with respect to the ground-state configuration in eV (for the supercell with 5 Ga and 5 As atoms as well as 12 Fe atoms). Contour lines are at a distance of 0.25 eV. The energy surface is calculated for the ideal atomic positions in plane whereas the ionic positions perpendicular to the interface have been relaxed.

Figure 6

(Color online) Formation energy for $\text{GaAs}/{\text{Fe}}_n/\text{GaAs}$ multilayers. Shown are ferromagnetic and the most favorable antiferromagnetic phase, respectively, compare Fig. 7.

Figure 7

(Color online) Energetically most favorable antiferromagnetic configuration for the periodically repeated Fe/GaAs system. The different colors of the Fe atoms indicate the orientation of the magnetic moments.

Figure 8

(Color online) Site-projected density of states. Top: Ideal interface for $\text{GaAs}/{\text{Fe}}_3/\text{GaAs}$. Center: Ideal interface for $\text{GaAs}/{\text{Fe}}_5/\text{GaAs}$. Bottom: 1/4 monolayer of Fe on the free surface in configuration a, see Fig. 2.