Marta Galicka

Method for suppression of stacking faults in Wurtzite III-V nanowires.

The growth of wurtzite GaAs and InAs nanowires with diameters of a few tens of nanometers with negligible intermixing of zinc blende stacking is reported. The suppression of the number of stacking faults was obtained by a procedure within the vapor-liquid-solid growth, which exploits the theoretical result that nanowires of small diameter ( approximately 10 nm) adopt purely wurtzite structure and are observed to thicken (via lateral growth) once the axial growth exceeds a certain length.

Modelling the structure of GaAs and InAs nanowires

Using ab initio methods, we study the stability of thin (diameters up to 10 nm) GaAs and InAs nanowires. Modelled nanowires were constructed using bulk atomic positions along six different crystallographic directions of either zinc-blende or wurtzite structures. Taking into account the reconstruction of the nanowire surfaces, we have found that, for diameters of up to 50 A, the most stable nanowires adopt the wurtzite (0001) structure—for such diameters the free energy of zinc-blende nanowires along any crystallographic axis is always larger than that of the wurtzite (0001) ones. To calculate the free energy in nanowires with larger diameters, we have approximated their total energy by the sum of congruous bulk and bulk surface energies. In these nanowires the interplay between the wurtzite and zinc-blende structures was demonstrated. The band structure and the density of charge in the nanowires have also been calculated.

Structure-Dependent Ferromagnetism in Mn-Doped III–V Nanowires

The electronic and magnetic properties of (Ga,Mn)As and (In,Mn)As nanowires are studied by ab initio methods. The results suggest that, in contrast to the bulk, in nanowires (In,Mn)As may exhibit better ferromagnetic behavior than (Ga,Mn)As. Moreover, the calculations show that in one-dimensional diluted magnetic semiconductors the distribution of Mn ions and the magnetic order depend crucially on the crystallographic structure. Since the growth of III-V nanowires of a given, either zinc blende or wurtzite, crystal structure is nowadays well controlled, these results can help to find the preferable material and conditions for the growth of ferromagnetic semiconductor nanowires.

Quantum spin Hall effect in IV-VI topological crystalline insulators

We envision that quantum spin Hall effect should be observed in

Giant Rashba Splitting in Pb1-xSnxTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk

(111)

Segregation of Impurities in GaAs and InAs Nanowires

-oriented thin films of SnSe and SnTe topological crystalline insulators. Using a tight-binding approach supported by first-principles calculations of the band structures we demonstrate that in these films the energy gaps in the two-dimensional band spectrum depend in an oscillatory fashion on the layer thickness. These results as well as the calculated topological invariant indexes and edge state spin polarizations show that for films ~20-40 monolayers thick a two-dimensional topological insulator phase appears. In this range of thicknesses in both, SnSe and SnTe, (111)-oriented films edge states with Dirac cones with opposite spin polarization in their two branches are obtained. While in the SnTe layers a single Dirac cone appears at the projection of the G point of the two-dimensional Brillouin zone, in the SnSe (111)-oriented layers three Dirac cones at M points projections are predicted.

Ferromagnetism in Mn‐doped III‐V Nanowires

The topological properties of lead-tin chalcogenide topological crystalline insulators can be widely tuned by temperature and composition. It is shown that bulk Bi doping of epitaxial Pb1-x Snx Te (111) films induces a giant Rashba splitting at the surface that can be tuned by the doping level. Tight binding calculations identify their origin as Fermi level pinning by trap states at the surface.

Quantum Spin Hall Effect in Strained (111)-Oriented SnSe Layers

Using ab initio methods based on density functional theory, we investigate the segregation and formation energies for various dopants (Si, Be, Zn, and Sn) commonly used to obtain p- or n-type conductivity in GaAs and InAs nanowires. The distribution of Au and O atoms, which may be unintentionally incorporated during the wire growth, is also studied. The calculations performed for nanowires of zinc blende and wurtzite structure show that the distribution of most of the impurities depends on the crystal structure of the wires. For example, it is shown that the same growth conditions can lead to lower energy for Si substituting Ga (donor) in the wire of wurtzite structure and substituting As (acceptor) in the wire of zinc blende structure. In contrast, we obtain that gold and oxygen atoms should always tend to stay at the lateral surfaces of GaAs and InAs nanowires, whereas for beryllium the lowest energies are found when the impurities are located in sites in the center of the wurtzite wire or along the [10...

Experimental and Theoretical Analysis οf PbTe-CdTe Solid Solution Grown by Physical Vapour Transport Method

Using ab initio methods based on the density functional theory, we study the stability of Mn‐doped GaAs and InAs nanowires as well as their electronic and magnetic properties. The model nanowires were constructed using bulk atomic positions of either zinc‐blende or wurtzite structures along (111) and (0001) crystallographic directions, respectively. The calculations show that in such one‐dimensional structures the distribution of Mn ions as well as their mutual spin alignment depends crucially on the crystallographic structure of the wire.

Defect Free PbTe Nanowires Grown by Molecular Beam Epitaxy on GaAs(111)B Substrates

Recently, the quantum spin Hall effect has been predicted in (111)-oriented thin films of SnSe and SnTe topological crystalline insulators. It was shown that in these films the energy gaps in the two-dimensional band spectrum depend in an oscillatory fashion on the layer thickness -- the calculated topological invariant indexes and edge state spin polarizations show that for films 20-40 monolayers thick a two-dimensional topological insulator phase appears. Edge states with Dirac cones with opposite spin polarization in their two branches are obtained for both materials. However, for all but the (111)-oriented SnTe films with an even number of monolayers an overlapping of bands in