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

Abstract

The effect of Mg codoping and Mg 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-à-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.

Ferromagnetism of cobalt-doped anatase TiO2 studied by bulk- and surface-sensitive soft x-ray magnetic circular dichroism

“…It was theoretically suggested [7] that the co-doping of magnetic semiconductors with shallow impurities affects the self-assembly of magnetic nanocrystals during epitaxy, and therefore modifies both the global and local magnetic behavior of the material. This concept was also qualitatively corroborated by experimental data for (Cd, Mn, Cr)Te [8] and (Ga, Mg, Fe)N [9][10][11]. However, origin of ferromagnetism at room-temperature is controversial so far.…”

Spinodal nanodecomposition in semiconductors doped with transition metals

“…Beyond dimers: The formations of larger TM cation clusters than dimers were considered and their magnetic properties assessed (Cui et al, 2007;Das et al, 2003;Gonzalez Szwacki et al, 2011;Hynninen et al, 2006b;Mahadevan et al, 2005;Navarro-Quezada et al, 2011;van Schilfgaarde and Mryasov, 2001). In this case (van Schilfgaarde and Mryasov, 2001),…”

Characterization of Fe-N nanocrystals and nitrogen–containing inclusions in (Ga,Fe)N thin films using transmission electron microscopy

“…Instead, they tend to accumulate in planes that lie perpendicular to the growth direction, either close to the film surface [4][5][6][7]13 or at its interface with the substrate, [14][15][16] by a process that is referred to as nucleation-controlled aggregation. 6,16 One of the consequences of TM aggregation is that high temperature ferromagnetism in many magnetically-doped semiconductors and oxides is now assigned to the presence of such aggregates. 1,2,17 According to other schools of thought, defects 15,18 and electron-mediated interactions 19 account for robust ferromagnetism in some cases.…”