356 research outputs found
Nucleation and Growth of GaN/AlN Quantum Dots
We study the nucleation of GaN islands grown by plasma-assisted
molecular-beam epitaxy on AlN(0001) in a Stranski-Krastanov mode. In
particular, we assess the variation of their height and density as a function
of GaN coverage. We show that the GaN growth passes four stages: initially, the
growth is layer-by-layer; subsequently, two-dimensional precursor islands form,
which transform into genuine three-dimensional islands. During the latter
stage, island height and density increase with GaN coverage until the density
saturates. During further GaN growth, the density remains constant and a
bimodal height distribution appears. The variation of island height and density
as a function of substrate temperature is discussed in the framework of an
equilibrium model for Stranski-Krastanov growth.Comment: Submitted to PRB, 10 pages, 15 figure
Spin injection from perpendicular magnetized ferromagnetic -MnGa into (Al,Ga)As heterostructures
Electrical spin injection from ferromagnetic -MnGa into an (Al,Ga)As
p-i-n light emitting diode (LED) is demonstrated. The -MnGa layers show
strong perpendicular magnetocrystalline anisotropy, enabling detection of spin
injection at remanence without an applied magnetic field. The bias and
temperature dependence of the spin injection are found to be qualitatively
similar to Fe-based spin LED devices. A Hanle effect is observed and
demonstrates complete depolarization of spins in the semiconductor in a
transverse magnetic field.Comment: 4 pages, 3 figure
Growth and optical properties of GaN/AlN quantum wells
We demonstrate the growth of GaN/AlN quantum well structures by
plasma-assisted molecular-beam epitaxy by taking advantage of the surfactant
effect of Ga. The GaN/AlN quantum wells show photoluminescence emission with
photon energies in the range between 4.2 and 2.3 eV for well widths between 0.7
and 2.6 nm, respectively. An internal electric field strength of
MV/cm is deduced from the dependence of the emission energy on the well width.Comment: Submitted to AP
Searching for physics beyond the Standard Model through the dipole interaction
The magnetic dipole interaction played a central role in the development of
QED, and continued in that role for the Standard Model. The muon anomalous
magnetic moment has served as a benchmark for models of new physics, and the
present experimental value is larger than the standard-model value by more than
three standard deviations. The electric dipole moment (EDM) violates parity
({}) and time-reversal ({}) symmetries, and in the context of the
theorem, the combination of charge conjugation and parity (). Since a new
source of {} violation outside of that observed in the and meson
systems is needed to help explain the baryon asymmetry of the universe,
searches for EDMs are being carried out worldwide on a number of systems. The
standard-model value of the EDM is immeasurably small, so any evidence for an
EDM would signify the observation of new physics. Unique opportunities exist
for EDM searches using polarized proton, deuteron or muon beams in storage
rings. This talk will provide an overview of the theory of dipole moments, and
the relevant experiments. The connection to the transition dipole moment that
could produce lepton flavor violating interactions such as is also mentioned.Comment: Invited Plenary talk at the 19th International Spin Physics
Symposium, Juelic
Self-assembled zinc blende GaN quantum dots grown
Zinc blende ~ZB! GaN quantum dots have been grown by plasma-assisted molecular-beam epitaxy
on AlN buffer layers using 3C-SiC~001! substrates. The two- to three-dimensional growth mode
transition is studied by following the evolution of the reflection high-energy electron diffraction
pattern. ZB GaN island layers are further examined by atomic force microscopy and transmission
electron microscopy, extracting a mean island height of 1.6 nm and a mean diameter of 13 nm at a
density of 1.331011 cm22. Embedded ZB GaN quantum dots show strong ultraviolet
photoluminescence without any thermal quenching up to room temperature.SFERERegion Rhône-AlpesConsejo Nacional de Ciencia y Tecnologí
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