Computational materials design for high-$T_c$ (Ga, Mn)As with Li codoping

Based on first-principles calculations and kinetic Monte Carlo simulations, we design a realistic and practical codoping technique for increasing the concentration of Mn atoms in GaAs and realizing high Curie temperatures in (Ga,Mn)As. We found that using codoping of Li interstitial atoms during the crystal growth has two great advantages. First, due to lower formation energy of Li interstitials compared to Mn interstitials, Li prevents formation of unwanted Mn interstitials. Second, Li interstitials can be removed by using post-growth annealing at low temperatures. This codoping method offers a general strategy to go far beyond the solubility limit and it should be applicable also to other diluted magnetic semiconductor systems.

Figure 1

Mixing energies as a function of Mn${}_S$ concentration $x$ for systems without and with interstitial atoms (Mn and Li, respectively).

Figure 2

Energy landscape from nudged elastic band (NEB) calculations for a diffusing Li${}_I^{+}$ (red filled circle) and Mn${}_I^{2+}$ (black filled squares) in GaAs along two tetrahedral interstitial sites $T_{\text{As}}$ (reaction coordinate 1) and $T_{\text{Ga}}$ (reaction coordinate 9), which are surrounded by four Ga and four As atoms, respectively, via a hexagonal interstitial site (reaction coordinate 5).

Figure 3

Energy landscape from nudged elastic band (NEB) calculations for a diffusing interstitial atom in proximity to Mn${}_S$ atoms. In (a) and (b), a Li${}_I$ is diffusing in proximity of 1 and 2 Mn${}_S$, respectively. In (c) and (d), a Mn${}_I$ is diffusing in proximity of 1 and 2 Mn${}_S$, respectively. The coordinates on the horizontal axis are listed in Table .

Figure 4

Graphical illustration of the pathway of the interstitial atom (gray) used for NEB calculations visualized on a two-dimensional plane. The Mn${}_S$ atoms are displayed in black and are fixed in the calculation. Part (a) shows the path with 1 Mn${}_S$ and (b) shows the case of 2 Mn${}_S$. The corresponding energy landscape is shown in Figs. 3a, 3b, 3c, 3d.

Figure 5

Binding energies of Li and Mn interstitials in presence to 1–4 Mn${}_S$ impurities. In the case of Mn${}_I$ interstitials, both the GGA and GGA + $U$ results are shown.