Dopant-assisted Concentration Enhancement of Substitutional Mn in Si and Ge Wenguang Zhu1,2,3, Zhenyu Zhang4,3 , and Efthimios Kaxiras1 1Department of Physics and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA

1
Dopant-assisted Concentration Enhancement of
Substitutional Mn in Si and Ge Wenguang
Zhu1,2,3, Zhenyu Zhang4,3 , and Efthimios
Kaxiras1 1Department 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
Dopant-assisted Concentration Enhancement of
Substitutional Mn in Si and Ge W. 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
Relative formation energy (Mn at substitutional vs. interstitial) Relative formation energy (Mn at substitutional vs. interstitial) Relative formation energy (Mn at substitutional vs. interstitial) Relative formation energy (Mn at substitutional vs. interstitial)
P As Sb Undoped
Si -0.84 -0.87 -0.81 0.58
Ge -1.35 -1.42 -1.42 -0.63
Physical Reason
Mn (p-type)
Coulomb attraction
Magnetic coupling between two Mn/As
substitutional pairs