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Diluted
magnetic semiconductors (DMS's), in which magnetic elements substitute
for a portion of host elements in semiconductor lattices, and their
heterostructures have attracted a great deal of interest because
of their favorable physical (or spin-electronic) properties for
applications in spin-related electronic devices such as optical
modulators, sensors, and memories. For many of these devices, it
is necessary to highly dope semiconductors. However, the high doping
of magnetic transition metals is extremely difficult with the commonly
used doping technique such as thermal diffusion because the solubility
of the magnetic impurities is too low, especially in III-V semiconductors
[1]. In order to achieve nonequilibrium crystal growth, Ohno and
co-workers [2] used low temperature molecular beam epitaxy and were
successfully able to achieve epitaxial growth of Mn-based III-V
DMS, (Ga,Mn)As with 110 K of Curie temperature. Subsequently, various
II-VI, III-V, and II-VI-V2 DMS's were discovered. More recently,
ferromagnetism was observed by Mn substitution in germanium [3],
a group-IV semiconductor. In this work, we have investigated possibility
of a new diluted ferromagnetic phase in cubic AlN, a III-V zinc-blende
semiconductor, by employing first-principles electronic-structure
calculations based on the density functional theory (DFT) with pseudopotential
approaches [4,5]. It was found that 3d transition metal (TM) elements
preferably substitutes for Al sites rather than N sites in cubic
AlN. Fe doped AlN showed the maximum magnetic moment, which is 5
$\mu_{B}$. More interestingly, all the transition metals (TM=V,
Cr, Mn, Fe, Co, Ni) used in this calculations exhibited half metallic
density of states where the Fermi energy lies in the energy gap
of the minority-spin states and thereby charge carriers are fully
spin-polarized at Fermi energy E$_{F}$. While the Fermi level is
located near the conduction band edge in the cases of Cr and Mn
doped DMS, the Fermi level of Co is located near the valence band
edge. The differences in the locations of Fermi level could be used
for band engineering. The detailed discussion of the availability
of TM doped AlN to the real situation will be addressed. |