The need for spin-injectors having the same zinc-blende-type crystal structure as conventional semiconductor substrates has created significant interests in theoretical predictions of possible metastable “half-metallic” zinc-blende ferromagnets, which are normally more stable in other structure-types, e.g., NiAs. Such predictions were based in the past on differences △bulk in the total energies of the respective bulk crystal (forms szinc blende and NiAs). We show here that the appropriate criterion is comparing difference △epi(as) in epitaxial total energies. This reveals that even if △bulk is small, still for MnAs, CrSb, CrAs, CrTe, △epi＞0 for all substrate lattice constant as, so the zinc-blende phase is not stabilized. For CrS we find △epi(as)＜0, but the system is antiferromagnetic, thus not half-metallic. Finally, zinc-blende CrSe is predicted to be epitaxially stable for as＞6.2 Å and is half metallic.

The wider-gap members of a semiconductor series such as diamond→Si→Ge or AlN→GaN→InN often cannot be doped n-type at equilibrium. We study theoretically if this is the case in the chalcopyrite family CuGaSe2→CuInSe2, finding that: (i) Bulk CuInSe2 (CIS, Eg=1.04 eV) can be doped at equilibrium n-type either by Cd or Cl, but bulk CuGaSe2 (CGS, Eg=1.68 eV) cannot; (ii) result (i) is primarily because the Cu-vacancy pins the Fermi level in CGS farther below the conduction band minimum than it does in CIS, as explained by the “doping limit rule; (iii) Cd doping is better than Cl doping, in that CdCu yields in CIS a higher net donor concentration than ClSe; and (iv) in general, the system shows massive compensation of acceptors (CdⅢ,VCu) and donors (ClSe,CdCu, InCud).

We report density-functional calculations of the ferromagnetic (FM) stabilization energy δ=EFM-EAFM for differently oriented Mn pairs in Ⅲ-V's (GaN, GaP, GaAs) and chalcopyrite (CuGaS2, CuGaSe2, CuGaTe2) semiconductors. Ferromagnetism is found to be the universal ground state (δ＜0) in all cases. The order of FM stability in Ⅲ–V’s is GaN＞GaP＞GaAs, whereas in chalcopyrites it is CuGaS2＞CuGaSe2＞CuGaTe2. Considering both groups, the order is GaN →GaP→GaAs→CuGaS2→CuGaSe2→GaSb≈CuGaTe2. The stronger FM stabilization in Ⅲ-V's is attributed to the stronger covalent coupling between the Mn 3d and the anion p orbitals. In contrast to expectations based on Ruderman-Kittel-(Kasuya)-Yosida, (i)all Mn-Mn pair separations show FM, with no FM to antiferromagnetic oscillations and, (ii) FM is orientationally dependent, with <110> Mn-Mn pairs being the most FM.

The electronic and magnetic properties of Mn doping at either cation sites in the class of Ⅰ-Ⅲ-Ⅵ2 chalcopyrites are studied by first-principles calculation. It is found that Mn doping at the Ⅲ site provides holes and stabilizes the ferromagnetic interaction between neutral Mn defects; the neutral MnoCu also stabilizes the ferromagnetism, although it provides electrons to the conduction band, instead of holes. The ferromagnetic stability is generally weaker when the cation or the anion becomes heavier in these chalcopyrites, i.e., along the sequences CuAlS2→CuGaS2→CuInS2 and CuGaS2→CuGaSe2→CuGaTe2. Interestingly, CuAlO2 in the chalcopyrite structure is predicted to have lower FM energy than CuAlS2 despite its lighter anion and shorter bonds. In general, Ⅲ site substitution gives stabler ferromagnetism than Cu substitution. Thus, the preferred growth conditions are Cu-rich and Ⅲ-poor, which maximize MnⅢ replacement. In n-type samples, when MnⅢ is negatively charged, the antiferromagnetic coupling is preferred. In p-type samples, the ground state of positively charged Mn+Cu is also antiferromagnetism. The main feature of the calculated electronic properties of Mn defect at either Cu or Ⅲ site is explained using a simple picture of dangling bond hybride and crystal-field resonance.

The quest for combining semiconducting with ferromagnetic properties has recently led to the exploration of Mn substitutions not only in binary (GaAs, CdTe), but also in ternary semiconductors such as chalcopyrites ABⅢX2Ⅵ. Here, however, Mn would substitute any of the two metal sites A or B. The site preference of Mn doping in CuMⅢX2Ⅵ chalcopyrite is crucial because it releases different type of carriers: electrons for substitution on the Cu sites, and holes for substitution on the MⅢ sites. Using first-principles calculation we show that Mn prefers the MⅢ site under Cu-rich and Ⅲ-poor conditions, and the Cu site under Ⅲ-rich condition. We establish the chemical potential domains for pure CuAlS2, CuGaS2, CuInS2, CuGaSe2, and CuGaTe2 stability. We show that the solubility of Mn on the MⅢ (Cu) site increases (decreases) as the Fermi level moves toward the conduction-band minimum (n-type conditions). It is further found that domains of chemical stability of all these chalcopyrites may be largely reduced by Mn incorporation.