N. Gonzalez Szwacki

Aggregation and magnetism of Cr, Mn, and Fe cations in GaN

A first-principles DFT-GGA+U study of the doping of GaN with Cr, Mn, or Fe confirms a strong tendency for the formation of embedded clusters occupying Ga sites of the wurtzite and zinc blende phases of GaN. Within the employed computation model, the tendency for aggregation is larger for Cr and Mn than for Fe. In contrast to previous DFT-GGA calculations, we predict a ferromagnetic ordering of the Cr and Mn clusters having more than two atoms while the Fe clusters are all antiferromagnetic. We have also investigated the magnetic ordering of nearest-neighboring ionic pairs that substitute gallium atoms at the (0001) wz-GaN surface. We find that Fe dopants tend to aggregate, whereas there is a repulsive interaction in the case of Cr and Mn. Nearest neighbor Mn and Fe pairs are coupled antiferromagnetically whereas the Cr pair is coupled ferromagnetically. The relevance of our finding to recent experimental findings is discussed.

The Fe-Mg interplay and the effect of deposition mode in (Ga,Fe)N doped with Mg

The effect of Mg codoping and its deposition mode on the Fe distribution in (Ga,Fe)N layers grown by metalorganic vapor phase epitaxy is investigated. Both homogeneously- and digitally-Mg codoped samples are considered and contrasted to the case of (Ga,Fe)N layers obtained without any codoping by shallow impurities. The structural analysis of the layers by high-resolution transmission electron microscopy and by high-resolution- and synchrotron x-ray diffraction gives evidence of the fact that in the case of homogenous-Mg doping, Mg and Fe competitively occupy the Ga-substitutional cation sites, reducing the efficiency of Fe incorporation. Accordingly, the character of the magnetization is modified from ferromagnetic-like in the non-codoped films to paramagnetic in the case of homogeneous Mg codoping. The findings are discussed vis-`a-vis theoretical results obtained by ab initio computations, showing only a weak effect of codoping on the pairing energy of two Fe cations in bulk GaN. However, according to these computations, codoping reverses the sign of the paring energy of Fe cations at the Ga-rich surface, substantiating the view that the Fe aggregation occurs at the growth surface. In contrast to the homogenous deposition mode, the digital one is found to remarkably promote the aggregation of the magnetic ions. The Fe-rich nanocrystals formed in this way are distributed non-uniformly, giving reason for the observed deviation from a standard superparamagnetic behavior.

(Ga,Mn)As under pressure: A first-principles investigation

Electronic and magnetic properties of

GaAs:N vs GaAs:B alloys: Symmetry-induced effects

{\mathrm{Ga}}_{1\ensuremath{-}}{}_{x}\text{Mn}{}_{x}\text{As}

The symmetry of the boron buckyball and a related boron nanotube

, obtained from first-principles calculations employing the hybrid HSE06 functional, are presented for

Iron in silicon: Interactions with radiation defects, carbon, and oxygen

x=6.25%

Interstitial Fe in Si and its interactions with hydrogen and shallow dopants

and 12.5% under pressures ranging from 0 to 15 GPa. In agreement with photoemission experiments at ambient pressure, we find for

Structural Properties of MnTe, ZnTe, and ZnMnTe

x=6.25%

Elastic Properties of Zinc Blende MnTe

that nonhybridized Mn

Energy decomposition analysis of metal silicide nanowires from first principles

3d