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Relation between structural, electronic, and magnetic properties in MOCVD grown (Ga,Fe)N, (Ga,Fe)N:Mg, and (Ga,Fe)N:Si
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Bonanni, Alberta1; Simbrunner, Clemens1; Li, Tian1; Navarro-Quezada, Andrea1; Wegscheider, Matthias1; Quast, Martin1; Kiecana, Michal2; Sawicki, Macjek2
1Austria;
2Poland |
It has recently been suggested that distinctive magnetic, magnetotransport, and magnetooptical properties of wide-band gap diluted magnetic semiconductors can be explained in terms of spinodal decomposition into regions with respectively a high and a low concentration of magnetic ions. Moreover, it has been argued that co-doping with acceptors or donors not only controls the carrier-mediated spin-spin interaction and influences the incorporation of magnetic ions in substitutional positions, but affects also the spinodal decomposition and the associated formation of nanocrystals with a high concentration of the magnetic constituent [1].
In order to test these ideas, we have undertaken studies of (Ga,Fe)N, (Ga,Fe)N:Mg, and (Ga,Fe)N:Si grown by metallorganic chemical vapour deposition. The obtained films have been characterized by high-resolution x-ray diffraction and secondary-ion mass spectroscopy as well as by transmission electron microscopy (TEM) and spatially-resolved energy dispersion x-ray spectroscopy (EDS) [2]. Our studies provide information on the dependence of nano-scale iron distribution on the iron-precursor flow-rate and co-doping. In particular, we reveal the growth-condition-dependent presence of wurtzite FeNx nanocrystals stabilized by the GaN host and showing segregation towards the film surface. We then clarify how the character of the distribution of the magnetic constituent affects macroscopic properties of (Ga,Fe)N, such as photoluminescence, Hall-effect, electron-spin resonance (ESR), and magnetic response examined in detail by a dedicated SQUID system [2]. In particular, in films containing sufficiently large nanocrystals, the magnetic response is dominated by a ferromagnetic-like characteristics persisting up to above 300 K. Actually, the temperature dependence of the spontaneous magnetization Ms, as determined from an Arrot plot analysis, shows that Ms can endure up to above 500 K. In these samples the Ms magnitude is found to depend on Mg co-odoping, corroborating the critical role of the Fermi level on the layer morphology. Furthermore, the non-uniform distribution of the nanocrystals along the growth direction promotes the coexistence of Fe in the 3+ state and electrons in the conduction band.
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