Transition Atom Impurities Research Articles

Ultra-fast diffusion mechanism of the late 3d transition metal impurities in silicon

Based upon ab initio electronic structure calculations with super-cells and an FLAPW method, we discuss the mechanism of the ultra-fast diffusion and the reduction of the migration barriers of the late 3d transition atom impurities of Co, Ni and Cu in silicon. The reduction mechanism of the migration barriers of the late 3d transition metal impurities is due to the pseudo-Jahn-Teller interaction, in which the six-fold-coordinated bonds are formed at the interstitial D 3d symmetry site and the energy gain by these bonds overcomes that of the four-fold-coordinated bonds at the tetrahedral T d interstitial site. For Sc, Ti, V, Cr, Mn and Fe impurities in silicon, the T d interstitial site is more stable than the D 3d site, however, for Co, Ni and Cu impurities, the D 3d interstitial site becomes more stable than the T d interstitial site. Calculated migration barriers are in reasonably good agreement with the experimental data. We discuss the systematic variation of the chemical trend of the migration barrier of 3d transition metal impurities in silicon based upon the calculation.

Change of Optical Absorption by Application of Electric Field in Al-CuAlS2-Au Diode

Planer type Schottky-type metal-semiconductor diodes were prepared using CuAlS2 single crystal with evaporated metal contacts of Al and Au. It is found that optical absorption spectra can be changed by application of the electrical field to the Al-CuAlS2-Au diode. This change in the absorption is attributed to the change in the valence of the transition atom impurities due to the movement of Fermi level caused by electric field.

Optical and ESR Characterization of Transition Atoms in CuAlS2

The optical and ESR properties of the CuAlS2 single crystals, doped with transition atom (TA) elements of the iron group, i.e. Ti, V, Cr, Mn, Fe, Co, and Ni, have been studied. It has been found that TA impurities in the CuAlS2 host lattice are present in their different valence states, the relative concentrations of these impurities in each valence state being dependent on the position of the Fermi level in the band gap of the host compound in relation to deep energy (demarcation) levels introduced by TA ions.

SPIN-POLARIZED ELECTRONIC STRUCTURE OF INTERSTITIAL 3d TRANSITION ATOM IMPURITIES IN SILICON

We review our recent results of the first principles calculation of the electronic structure of interstitial 3d transition atom impurities in silicon using the impurity Green’s function method and full-potential linearized augmented plane wave (FLAPW) method. We give a unified physical picture to the hyperfine and superhyperfine interaction data, g-values, spin-multiplets, donor and acceptor ionization transition energies, and spin-lattice relaxation time, comparing with the available experimental data.

Self-consistent one-electron states of substitutional and interstitial 5d transition-atom impurities in silicon.

The electronic structure of the 5d transition-metal impurities Hg, Au, Pt, Ir, Os, Re, and W in silicon has been studied theoretically within the framework of a nonrelativistic self-consistent one-particle model. The energy spectra of the substitutional and tetrahedral-site interstitial neutral atoms have been obtained by using the Watson-sphere-terminated multiple-scattering X\ensuremath{\alpha} molecular cluster method. The role played by the metal 5d states in the formation of impurity levels within the crystal band gap and resonances in the valence band has been established. The observed chemical trends of the impurity level positions for the 5d elements are analyzed and compared with those inferred from previous cluster and Green's-function calculations for the 3d transition-metal series. The results of our one-electron theory provide a good description of the observed physical properties of the widely studied Au and Pt impurities in silicon. A good correlation between our calculations and the sparse data which are available for Hg, Ir, Os, Re, and W has been established.

Theory of 3d Transition Atom Impurities in Semiconductors

The utility of semiconductors in many device applications, such as high­ speed logic circuits ( 1-2), optoelectronic devices (3-4), microwave devices (5), and solar cells (6), rests on the characteristics of the intentionally introduced impurities (dopants) as much as on the properties of trace amounts of unintentional contaminations. Transition atom (T A) impurities in semiconductors form a special class of such contaminants. They were studied experimentally in great detail (e.g. review articles in References 7-10) using a broad range of techniques, including optical absorption, luminescence, photocapacitance, photoconductivity, electron para­ magnetic resonance (EPR), electron nuclear double resonance (ENDOR), deep level transient spectroscopy (DLTS), and Hall effect. This review article is concerned with the theoretical understanding of the electronic properties of T A impurities in Si, III-V, and II-VI semiconductors. First, we establish the nomenclature. When a transition atom takes up a substitutional site, say on a cation, its formal oxidation state when neutral (labeled A 0) becomes that of the site it replaces, e.g. T A 3 + if it replaces a column III element. When the impurity captures an electron its charge state becomes negative (denoted A ), and the oxidation state is TA2+. Conversely, when the impurity loses an electron its charge state becomes positive (labeled A +), and the oxidation state becomes TA4+. The tenfold degenerate atomic d orbitals can split in the cubic environment into a

Electronic structure of transition-atom impurities in GaP.

We describe the elements of the electronic structure and the chemical trends in cation-substitutional Cr, Mn, Fe, Co, Ni, Cu, and Zn impurities in GaP and Fe in InP. First, using the recently developed method of Fazzio, Caldas, and Zunger, we deconvolute the observed acceptor, donor, and intracenter d..-->..d( excitation energies into a one-electron mean-field contribution and a many-electron multiplet correction. Then, using the self-consistent quasiband crystal-field Green's-function method of Lindefelt and Zunger, we show that one-electron theory explains the magnitudes and the trends in the mean-field part of the observed transition energies (evaluated as differences in total energies). Many-electron contributions are found to be sizable, and are responsible for the nonmonotonic trends of the observed acceptor energies with the impurity's atomic number and a reduction in the Mott-Hubbard Coulomb energies. We discuss in detail the impurity-induced energy levels (gap states as well as resonances), the photoionization and intracenter excitations, the attenuation of the Mott-Hubbard Coulomb repulsion energies with the attendant plurality of charge states, the self-regulating response of the electron density to excitations, and the nature of the transition-atom--host chemical bond with its relationship to the structure of bulk 3d phosphides.

Theory of 3d Transition Atom Impurities in Semiconductors

Gallium is a metal that literally melts in your hand. It has low toxicity, near-zero vapor pressure, and a viscosity similar to water. Despite possessing a surface tension larger than any other liquid (near room temperature), gallium can form nonspherical ...Read More

Interstitial transition atom impurities in silicon: electronic structure and lattice relaxation

Both the electronic structure and the `breathing-mode' relaxation for tetrahedral interstitial 3D transition atom impurities in silicon are studied in the local-density approximation. The calculations show that although the interstitial 3d impurities constitute a very large perturbation locally, they interact rather weakly with the surrounding crystal in the sense that they perturb the spatial distribution of electrons on the surrounding atoms only weakly. A special pattern of relaxation is predicted, with an outward relaxation of the first-nearest neighbours and an inward relaxation of the second-nearest neighbours. It is explained in terms of the impurity-induced charge rearrangement.(19 refs)

Applicability of the local-density theory to interstitial transition-metal impurities in silicon

It is shown that the local-density formalism does not describe correctly the symmetry of the many-electron ground state of unrelaxed interstitial transition-atom impurities in silicon, but that a self-interaction correction to it produces the observed ground-state symmetries.

Electronic structure of substitutional 3d transition atom impurities in silicon

We report the results of a self-consistent calculation within the local density approximation for all the substitutional 3d transition atom (TA) impurities in an extended silicon host crystal using the quasi band Green's function method. Chemical trends in the gap state energies and 3d-line resonances are discussed as well as trends in the effective electronic configuration of TA impurities. An explanation for the remarkable property that many different charged states of TA impurities exist in the narrow band gap, despite the fact that the corresponding ionized states of the free TA span a range of ∼ 60 eV, is proposed.

Phenomenology of solid solubilities and ion-implantation sites: An orbital-radii approach

The crossing points of the first-principles nonlocal screened atomic pseudopotentials of the elements were shown previously to constitute a sensitive anisotropic atomic-size scale. This scale allows systematization of the crystal structure of as many as 565 binary compounds A. Zunger, [Phys. Rev. B 22, 5839 (1980)]. In this paper we apply the same coordinates for systematizing the trends in the solid solubilities in the divalent solvents Be, Mg, Zn, Cd, Hg, and in the semiconductor solvents Si and Ge (192 data points), as well as the location of the ion-implantation sites in Be and Si (60 data points). We find that these nonempirical and atomic coordinates produce a systematization of the data that overall is equal to or better than that produced by the empirical coordinates of Miedema and Darken-Gurry which are derived from properties of the condensed phases. Furthermore, it is found that the orbital-radii coordinates which incorporate directly the effects of only the $s$ and $p$ atomic orbitals are capable of predicting the solubility trends and ion-implantation sites even for the (nonmagnetic) transition atom impurities.

Magnetic and Crystallographic Study on the Electronic State of Interstitial Cations in MnSb

Ferromagnetic compounds Mn 1+δ Sb with NiAs crystal structure have a wide existing range (0≤δ≤0.22). Compounds of Mn 1.05 M δ Sb (M=Cr, Fe and Co) are prepared in order to study the electronic state of excess Mn in Mn 1+δ Sb. It is found that the excess cations occupy the same interstitial site as Mn, and have 0 µ B for the case of M=Cr and Mn and about 1 µ B for M=Fe and Co, and that they reduce the total magnetization and the Curie temperature at about the same rate as the case of M=Mn. A qualitative discussion is given on the analogy of transition atom impurities in metals.