Optimization of Mn doping in group-IV-based dilute magnetic semiconductors by electronic codopants

Abstract

The percentage of substitutional doping of magnetic atoms (Mn) in group-IV-based dilute magnetic semiconductors (DMS) can be increased by co-doping with another conventional electronic dopant (e-dopant), as demonstrated from first-principles calculations recently [Zhu et al., Phys. Rev. Lett. 100, 027205 (2008)]. Here, we report extensive theoretical investigations of the kinetic and thermodynamic characteristics of several co-doped systems including bulk Si and Ge as hosts and various group-III and group-V e-dopants. The main findings are as follows: The n-p pairing of n-type e-dopants with p-type substitutional Mn is energetically stable in bulk Ge and Si. Mn atoms move from interstitial sites to substitutional sites easier (with lower kinetic barriers) in the presence of a neighboring n-type e-dopant. Magnetic coupling between two Mn atoms in bulk Ge oscillates between positive (ferromagnetic) and negative (antiferromagnetic) values with increasing Mn-Mn distance, but in Mn/As co-doped Ge the coupling parameter remains positive at all distances beyond nearest-neighbors and this qualitative difference does not change with the doping level. For Mn doped Si, all coupling values except for the nearest neighbor one are positive and do not change much upon co-doping. We find an unconventional magnetic anisotropy in the co-doped system, that is, the dependence of magnetic coupling on the relative positions of the magnetic ions and their neighboring e-dopants. We map the calculated magnetic coupling to a classical Heisenberg model and employ Monte Carlo simulations to estimate the Curie temperature (Tc). We find that in Mn doped Ge no ferromagnetic order exists for Mn concentrations ranging from 3.13% to 6%. Instead, a spin-glass phase transition occurs at ∼5 K at 5% Mn doping. For Mn/As co-doped Ge, Tc increases nearly linearly with the Mn concentration and reaches 264 K at 5% Mn doping.

Induced magnetism on silicon in Fe3Si quasi-Heusler compound

“…7 display that the density functional calculations using the perfect D0 3 structure reproduce very well the experimental data, in particular the XMCD. It is well known [22][23][24] that XMCD spectra of dia-or paramagnetic elements with induced ferromagnetism in an alloy can be utilized to characterize atomic arrangements since their spectroscopic features are highly sensitive to the change in interactions with ferromagnetic species. It is reasonable to conclude that the Fe 3 Si films used in the experiment consist mainly of D0 3 symmetry.…”

Ferromagnetism in Mn-implanted epitaxially grown Ge on Si(100)

“…One promising material system is Mn-doped Ge because of its compatibility with Si processing. Theoretical studies show that Mn dopants will prefer to occupy substitutional sites in a crystalline Ge lattice [2] and one can optimize Mn doping by adding other codopants [3,4]. Theoretical modeling also predicts enhanced magnetic properties and higher solubility of Mn-doped amorphous Si and Ge systems [5].…”

Influence of n+ and p+ doping on the lattice sites of implanted Fe in Si

“…More recently TM-doped silicon has also attracted attention as a possible magnetic semiconductor system. The magnetic properties of TMs in Si are expected to depend on whether the TMs are incorporated substitutionally or interstitially and based on first principle calculations it was proposed that the position of the Fermi level (which depends on n-or p-doping) and the availability of vacancies are of crucial importance in controlling the lattice site [7][8][9][10][11][12] . Most of the theoretical work on this subject concerned Mn in Si, but also Fe was addressed 9,12 .…”