Initial state: Mn at interstitial neighboring with a substitutional As Final state:

1. Dopant-assisted Concentration Enhancement of Substitutional Mn in Si and GeWenguang Zhu1,2,3, Zhenyu Zhang4,3 , and Efthimios Kaxiras11Department of Physics and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 021382Center for Computational Materials, University of Texas, Austin, Texas 787123Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 379964Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 Diluted magnetic semiconductors (DMS) provide a fascinating platform for fundamental studies of ferromagnetic ordering mechanisms, and they have been considered as promising materials for spintronic devices. However, the low Curie temperature of ferromagnetic ordering remains one of the main obstacles for potential device applications of DMS. Extensive theoretical and experimental studies indicate that the Curie temperature of DMS depends sensitively on the ability of magnetic dopants to occupy substitutional versus interstitial sites. For Group-IV semiconductors, the thermodynamics solubility of magnetic dopants is extremely low. We propose a novel co-doping strategy to enhance the doping concentration of the magneric dopants in host Group-IV semiconductors by introducing traditional Group-III and Group-V electronic dopants. The influence of p- and n-type electronic dopants on Mn incorporation in bulk Si and Ge was studied using first-principles calculations within density functional theory. In Si, it is found that the site preference of a single Mn atom is reversed from interstitial to substitutional in the presence of a neighboring n-type dopant. In Ge, a Mn atom is more readily incorporated into the lattice when an n-type dopant is present in its immediate neighborhood, forming a stable Mn/dopant pair with both impurities at substitutional sites. A detailed analysis of the magnetic exchange interactions between such pairs reveals a dramatic enhancement in the anisotropy of the magnetic coupling within the systems. [1] W. Zhu, Z. Y. Zhang, and E. Kaxiras, Phys. Rev. Lett. 100, 027205 (2008).

2. 1.06 without As Ge 0.82 with As Ge Mn 0.25 As As Mn 0.05 Ge Ge n-type dopant Dopant-assisted Concentration Enhancement of Substitutional Mn in Si and GeW. Zhu, Z. Y. Zhang, and E. Kaxiras, Phys. Rev. Lett. 100, 027205 (2008). Initial State Final State Initial state: Mn at interstitial neighboring with a substitutional As Final state: Mn dives into substitutional by kicking out a host Ge atom next to the substitutional As Anisotropy Physical Reason Mn (p-type) Coulomb attraction Magnetic coupling between two Mn/As substitutional pairs