115 research outputs found
Axial GaAs/Ga(As,Bi) Nanowire Heterostructures
Bi-containing III-V semiconductors constitute an exciting class of metastable
compounds with wide-ranging potential optoelectronic and electronic
applications. However, the growth of III-V-Bi alloys requires group-III-rich
growth conditions, which pose severe challenges for planar growth. In this
work, we exploit the naturally-Ga-rich environment present inside the metallic
droplet of a self-catalyzed GaAs nanowire to synthesize metastable
GaAs/GaAsBi axial nanowire heterostructures with
high Bi contents. The axial GaAsBi segments are
realized with molecular beam epitaxy by first enriching only the
vapor-liquid-solid (VLS) Ga droplets with Bi, followed by exposing the
resulting Ga-Bi droplets to As at temperatures ranging from 270 to
380\,^{\circ}C to precipitate GaAsBi only under
the nanowire droplets. Microstructural and elemental characterization reveals
the presence of single crystal zincblende GaAsBi
axial nanowire segments with Bi contents up to (102). This work
illustrates how the unique local growth environment present during the VLS
nanowire growth can be exploited to synthesize heterostructures with metastable
compounds
Lattice parameters of ScAlN layers grown on GaN(0001) by plasma-assisted molecular beam epitaxy
An accurate knowledge of the lattice parameters of the new nitride
ScAlN is essential for understanding the elastic
and piezoelectric properties of this compound as well as for the ability to
engineer its strain state in heterostructures. Using high-resolution x-ray
diffractometry, we determine the lattice parameters of 100-nm-thick undoped
ScAlN layers grown on GaN(0001) templates by
plasma-assisted molecular beam epitaxy. The Sc content of the
layers is measured independently by both x-ray photoelectron spectroscopy and
energy-dispersive x-ray spectroscopy and ranges from 0 to 0.25. The in-plane
lattice parameter of the layers linearly increases with increasing
, while their out-of-plane lattice parameter remains constant.
Layers with 0.09 are found to be lattice matched to GaN,
resulting in a smooth surface and a structural perfection equivalent to that of
the GaN underlayer. In addition, a two-dimensional electron gas is induced at
the ScAlN/GaN heterointerface, with the highest
sheet electron density and mobility observed for lattice-matched conditions
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Light coupling between vertical III-As nanowires and planar Si photonic waveguides for the monolithic integration of active optoelectronic devices on a Si platform
We present a new concept for the optical interfacing between vertical III-As nanowires and planar Si waveguides. The nanowires are arranged in a two-dimensional array which forms a grating structure on top of the waveguide. This grating enables light coupling in both directions between the components made from the two different material classes. Numerical simulations show that this concept permits a light extraction efficiency from the waveguide larger than 45% and a light insertion efficiency larger than 35%. This new approach would allow the monolithic integration of nanowire-based active optoelectronics devices, like photodetectors and light sources, on the Si photonics platform
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