91 research outputs found
Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain
Electronic structures of wurtzite GaAs nanowires in the [0001] direction were
studied using first-principles calculations. It was found that the band gap of
GaAs nanowires experience a direct-to-indirect transition when the diameter of
the nanowires is smaller than ~28 {\AA}. For those thin GaAs nanowires with an
indirect band gap, it was found that the gap can be tuned to be direct if a
moderate external uniaxial strain is applied. Both tensile and compressive
strain can trigger the indirect-to-direct gap transition. The critical strains
for the gap-transition are determined by the energy crossover of two states in
conduction bands.Comment: 4 pages, 4 figure
Chemical scissors cut phosphorene nanostructures and their novel electronic properties
Phosphorene, a recently fabricated two dimensional puckered honeycomb
structure of phosphorus, showed promising properties for applications of
nano-electronics. In this work, we report our findings of chemical scissors
effects on phosphorene, using first principles density functional theory
methods. It was found that several chemical species, such as H, F, Cl and OH
group, can act effectively as scissors to cut phosphorene. Phosphorus chains
and nanoribbons can be obtained using different surface coverage of the
chemical species. The scissor effects of these species are resulted from their
strong chemical bonds with the P atoms. Species such as O, S and Se were not
able to cut phosphorene nanostructures due to their lack of strong binding with
P. The electronic structure calculations of the produced P-chains reveal that
the saturated chain is an insulator while the pristine chain demonstrates a
Dirac point at X with a Fermi velocity of 8*10E5 m/s. The obtained zigzag
phosphorene nanoribbons show either metallic or semiconducting behaviors,
depending on the treatment of the edge P atoms.Comment: 14 pages, 7 figures, 1 table. arXiv admin note: text overlap with
arXiv:1404.599
Electronic Properties of Strained Si/Ge Core-Shell Nanowires
We investigated the electronic properties of strained Si/Ge core-shell
nanowires along the [110] direction using first principles calculations based
on density-functional theory. The diameter of the studied core-shell wire is up
to 5 nm. We found the band gap of the core-shell wire is smaller than that of
both pure Si and Ge wires with the same diameter. This reduced band gap is
ascribed to the intrinsic strain between Ge and Si layers, which partially
counters the quantum confinement effect. The external strain is further applied
to the nanowires for tuning the band structure and band gap. By applying
sufficient tensile strain, we found the band gap of Si-core/Ge-shell nanowire
with diameter larger than ~3 nm experiences a transition from direct to
indirect gap.Comment: 4 figure
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