294 research outputs found
Correlation effects in the density of states of annealed GaMnAs
We report on an experimental study of low temperature tunnelling in hybrid
NbTiN/GaMnAs structures. The conductance measurements display a root mean
square V dependence, consistent with the opening of a correlation gap in the
density of states of GaMnAs. Our experiment shows that low temperature
annealing is a direct empirical tool that modifies the correlation gap and thus
the electron-electron interaction. Consistent with previous results on
boron-doped silicon we find, as a function of voltage, a transition across the
phase boundary delimiting the direct and exchange correlation regime.Comment: Replaced with revised version. To appear in Phys. Rev.
Electronic and magnetic properties of GaMnAs: Annealing effects
The effect of short-time and long-time annealing at 250C on the conductivity,
hole density, and Curie temperature of GaMnAs single layers and GaMnAs/InGaMnAs
heterostructures is studied by in-situ conductivity measurements as well as
Raman and SQUID measurements before and after annealing. Whereas the
conductivity monotonously increases with increasing annealing time, the hole
density and the Curie temperature show a saturation after annealing for 30
minutes. The incorporation of thin InGaMnAs layers drastically enhances the
Curie temperature of the GaMnAs layers.Comment: 4 pages, 6 figures, submitted to Physica
Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As
The effect of annealing at 250 C on the carrier depth profile, Mn
distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As
layers with thicknesses > 200 nm, grown by molecular-beam epitaxy at low
temperatures, is studied by a variety of analytical methods. The vertical
gradient in hole concentration, revealed by electrochemical capacitance-voltage
profiling, is shown to play a key role in the understanding of conductivity and
magnetization data. The gradient, basically already present in as-grown
samples, is strongly influenced by post-growth annealing. From secondary ion
mass spectroscopy it can be concluded that, at least in thick layers, the
change in carrier depth profile and thus in conductivity is not primarily due
to out-diffusion of Mn interstitials during annealing. Two alternative possible
models are discussed.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
Enhancement of the Curie temperature in GaMnAs/InGaMnAs superlattices
We report on an enhancement of the Curie temperature in GaMnAs/InGaMnAs
superlattices grown by low-temperature molecular beam epitaxy, which is due to
thin InGaMnAs or InGaAs films embedded into the GaMnAs layers. The pronounced
increase of the Curie temperature is strongly correlated to the In
concentration in the embedded layers. Curie temperatures up to 110 K are
observed in such structures compared to 60 K in GaMnAs single layers grown
under the same conditions. A further increase in T up to 130 K can be
achieved using post-growth annealing at temperatures near the growth
temperature. Pronounced thickness fringes in the high resolution X-ray
diffraction spectra indicate good crystalline quality and sharp interfaces in
the structures.Comment: 4 pages, 4 figures, submitted to Appl. Phys. Let
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