arXiv subjects

J. Masek

Publications and source records attributed to J. Masek.

24 records · Page 2Linked to original sources

arXiv2003

Ferromagnetic transition temperature enhancement in (Ga,Mn)As semiconductor by carbon co-doping

We present a theoretical study of (Ga,Mn)(As,C) diluted magnetic semiconductors with high C acceptor density that combines insights from phenomenological model and microscopic approaches. A tight-binding coherent potential approximation is used to describe the electronic structure in the presence of Mn$_{\rm Ga}$ and C$_{\rm As}$ impurities. We find only a small effect of C on the distribution and coherence of electronic states close to the top of the valence band and on the coupling between Mn moments, even at doping levels of several per cent. These results justify applying the model of ferromagnetic Mn-Mn coupling mediated by itinerant holes in the valence band also to C doped samples. The increase of ferromagnetic transition temperature due to the presence of C acceptors is illustrated by calculations that use the k.p Kohn-Luttinger description of the GaAs valence band and assume systems where Mn local moment and itinerant hole densities can be varied independently.

cond-mat.mtrl-sci↗

arXiv2003

Ab initio study of Curie temperatures of diluted III-V magnetic semiconductors

The electronic structure of diluted (Ga,Mn)As magnetic semiconductors in the presence of As-antisites and magnetic disorder is studied within the framework of the local spin density approximation. Both the chemical and magnetic disorders are treated using the coherent potential approximation. A ground state with partial disorder in the local moments and with a reduced total magnetic moment appears in the presence of As-antisites. We first estimate the Curie temperature T_c from total energy differences between the ferromagnetic and the paramagnetic state by identifying these with the corresponding energy difference in a classical Heisenberg model. A more systematic approach within the framework of the mean-field approximation to estimate T_c consists in an evaluation of the effective exchange fields acting on the magnetic moment at a given site. The presence of As-antisites strongly reduces the Curie temperature. The results indicate that the effect of impurities on the electronic structure cannot be neglected and influences the Curie temperature non-negligibly. A comparison of the calculated Curie temperatures to existing experimental data indicates an increase of the donor concentration with the increase of the Mn-content.

cond-mat.mtrl-sci↗

arXiv2003

Correlated Doping in Semiconductors: The Role of Donors in III-V Diluted Magnetic Semiconductors

We investigate the compositional dependence of the total energy of the mixed crystals (Ga,Mn)As co-doped with As, Sn, and Zn. Using the ab initio LMTO-CPA method we find a correlation between the incorporation of acceptors (Mn, Zn) and donors (Sn, antisite As). In particular, the formation energy of As_Ga is reduced by approx. 0.1 eV in the presence of Mn, and vice versa. This leads to the self-compensating behavior of (Ga,Mn)As.

cond-mat.mtrl-sci↗

arXiv2003

Disorder-Induced Effects in III-V Semiconductors with Mn

The substitution of Mn in the III-V diluted magnetic semiconductors leads to a strong electron scattering on impurities. Besides the features induced in the valence band by the hybridization with the Mn d-states, also the conduction band is affected by the absence of the Mn s-states at its edge. Also the high concentration of compensating donors modifies the band structure. This is shown on the absorption coefficient epsilon2(omega) of GaP doped with Mn and Se. The absorption evaluated by ab initio density functional calculations starts with a smooth tail and does not show the structure typical for III-V materials. We analyze these features and the role of the donors on model systems using the tight-binding coherent potential approach.

cond-mat.mtrl-sci↗

arXiv2003

Lattice constant in diluted magnetic semiconductors (Ga,Mn)As

We use the density-functional calculations to investigate the compositional dependence of the lattice constant of (Ga,Mn)As containing various native defects. The lattice constant of perfect mixed crystals does not depend much on the concentration of Mn. The lattice parameter increases if some Mn atoms occupy interstitial positions. The same happens if As antisite defects are present. A quantitative agreement with the observed compositional dependence is obtained for materials close to a complete compensation due to these two donors. The increase of the lattice constant of (Ga,Mn)As is correlated with the degree of compensation: the materials with low compensation should have lattice constants close to the lattice constant of GaAs crystal.

cond-mat.mtrl-sci↗

arXiv2002

Self-compensating incorporation of Mn in Ga(1-x)Mn(x)As

We consider hypothetical Ga7MnAs8, Ga16MnAs16, and Ga14Mn3As16 crystals with Mn in a substitutional, interstitial, and both positions. Spin-polarized FPLAPW calculations were used to obtain their electronic structure. We show that the interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional positions. This explains why the number of holes in Ga(1-x)Mn(x)As is much smaller than x. The presence of interstitial atoms may also be the reason for the lattice expansion with increasing content of Mn. The differences in electronic behavior of substitutional and interstitial Mn are discussed.

cond-mat.mtrl-sci↗