86 research outputs found
Ferromagnetic GaâËâ Mnâ As produced by ion implantation and pulsed-laser melting
We demonstrate the formation of ferromagneticGaâËâMnâAsfilms by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of xâ0.03. A remanent magnetization persisting above 85 K has been observed for samples with xâ0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in GaâËâMnâAs is rather robust to the presence of structural defects.The work at the Lawrence Berkeley National Laboratory
was supported by the Director, Office of Science, Office of
Basic Energy Sciences, Division of Materials Sciences and
Engineering, of the U.S. Department of Energy under Contract
No. DE-AC03-76SF00098. The work at Harvard was
supported by NASA Grant No. NAG8-1680. One of
the authors ~M.A.S.! acknowledges support from an NSF
Graduate Research Fellowship
Electronic structure of ferromagnetic semiconductor Ga1-xMnxAs probed by sub-gap magneto-optical spectroscopy
We employ Faraday and Kerr effect spectroscopy in the infrared range to
investigate the electronic structure of Ga1-xMnxAs near the Fermi energy. The
band structure of this archetypical dilute-moment ferromagnetic semiconductor
has been a matter of controversy, fueled partly by previous measurements of the
unpolarized infrared absorption and their phenomenological impurity-band
interpretation. The infrared magneto-optical effects we study arise directly
from the spin-splitting of the carrier bands and their chiral asymmetry due to
spin-orbit coupling. Unlike the unpolarized absorption, they are intimately
related to ferromagnetism and their interpretation is much more microscopically
constrained in terms of the orbital character of the relevant band states. We
show that the conventional theory of the disordered valence band with dominant
As p-orbital character and coupled by kinetic-exchange to Mn local moments
accounts semi-quantitatively for the overall characteristics of the measured
infrared magneto-optical spectra.Comment: 4 pages 3 figure
Compensation-dependent in-plane magnetization reversal processes in Ga1-xMnxP1-ySy
We report the effect of dilute alloying of the anion sublattice with S on the
in-plane uniaxial magnetic anisotropy and magnetization reversal process in
Ga1-xMnxP as measured by both ferromagnetic resonance (FMR) and superconducting
quantum interference device (SQUID) magnetometry. At T=5K, raising the S
concentration increases the uniaxial magnetic anisotropy between in-plane
directions while decreasing the magnitude of the (negative) cubic anisotropy
field. Simulation of the SQUID magnetometry indicates that the energy required
for the nucleation and growth of domain walls decreases with increasing y.
These combined effects have a marked influence on the shape of the
field-dependent magnetization curves; while the direction remains the easy axis
in the plane of the film, the field dependence of the magnetization develops
double hysteresis loops in the [011] direction as the S concentration increases
similar to those observed for perpendicular magnetization reversal in lightly
doped Ga1-xMnxAs. The incidence of double hysteresis loops is explained with a
simple model whereby magnetization reversal occurs by a combination of coherent
spin rotation and noncoherent spin switching, which is consistent with both FMR
and magnetometry experiments. The evolution of magnetic properties with S
concentration is attributed to compensation of Mn acceptors by S donors, which
results in a lowering of the concentration of holes that mediate
ferromagnetism.Comment: 37 pages, 9 figures, 3 table
Diluted II-VI Oxide Semiconductors with Multiple Band Gaps
We report the realization of a new multi-band-gap semiconductor. The highly
mismatched alloy Zn1-yMnyOxTe1-x has been synthesized using the combination of
oxygen ion implantation and pulsed laser melting. Incorporation of small
quantities of isovalent oxygen leads to the formation of a narrow,
oxygen-derived band of extended states located within the band gap of the
Zn1-yMnyTe host. When only 1.3% of Te atoms is replaced with oxygen in a
Zn0.88Mn0.12Te crystal (with band gap of 2.32 eV) the resulting band structure
consists of two direct band gaps with interband transitions at ~1.77 eV and 2.7
eV. This remarkable modification of the band structure is well described by the
band anticrossing model in which the interactions between the oxygen-derived
band and the conduction band are considered. With multiple band gaps that fall
within the solar energy spectrum, Zn1-yMnyOxTe1-x is a material perfectly
satisfying the conditions for single-junction photovoltaics with the potential
for power conversion efficiencies surpassing 50%.Comment: 12 pages, 4 figure
THz Transient Photoconductivity of the III-V Dilute Nitride GaPAsN
THz Time-Resolved Photoconductivity is used to probe carrier dynamics in the
dilute III-V nitride GaP0.49As0.47N0.036. In these measurements a femtosecond
optical pump-pulse excites electron-hole pairs, and a delayed THz pulse
measures the change in conductivity. We find the photoconductivity is dominated
by localized carriers. The decay of photoconductivity after excitation is
consistent with bimolecular electron-hole recombination with recombination
constant r = 3.2E-8 +/-0.8E-8 cm3/s. We discuss the implications for
applications in solar energy.Comment: 12 pages, 4 figure
Fabrication of GaNxAs1-x Quantum Structures by Focused Ion Beam Patterning
A novel approach to the fabrication of GaNxAs1-x quantum dots and wires via
ion beam patterning is presented. Photomodulated reflectance spectra confirm
that N can be released from the As sublattice of an MBE-grown GaNxAs1-x film by
amorphization through ion implantation followed by regrowth upon rapid thermal
annealing (RTA). Amorphization may be achieved with a focused ion beam (FIB),
which is used to implant Ga ions in patterned lines such that annealing
produces GaAs regions within a GaNxAs1-x film. The profiles of these amorphized
lines are dependent upon the dose implanted, and the film reaches a damage
threshold during RTA due to excess Ga. By altering the FIB implantation
pattern, quantum dots or wires may be fabricated.Comment: To appear in the proceedings of the 27th International Conference on
the Physics of Semiconductors (ICPS-27, Flagstaff, AZ, July 26-30, 2004
Mutual passivation of group IV donors and nitrogen in diluted GaNâAsâËâ alloys
We demonstrate the mutual passivation phenomenon of Ge donors and isovalent N in highly mismatched alloy GaNâAsâËâdoped with Ge. Layers of this alloy were formed by the sequential implantation of Ge and N ions followed by pulsed laser melting and rapid thermal annealing. The mutual passivation effect results in the electrical deactivation of GeGa donors (Ge on Ga sites) and suppression of the NAs (N on As sites) induced band gap narrowing through the formation of GeGaâNAs nearest neighbor pairs. These results in combination with the analogous effect observed in Si-doped GaNâAsâËâ provide clear evidence of the general nature of the mutual passivation phenomenon in highly mismatched semiconductor alloys.This work was supported by the Director, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences and Engineering, U.S. Department of Energy, under
Contract No. DE-AC03-76SF00098. One of the authors
~M.A.S.! acknowledges support by an NSF graduate research
fellowship
Mn L3,2 X-ray Absorption Spectroscopy And Magnetic Circular Dichroism In Ferromagnetic (Ga,Mn)P
We have measured the X-ray absorption (XAS) and X-ray magnetic circular
dichroism (XMCD) at the Mn L3,2 edges in ferromagnetic Ga1-xMnxP films for
0.018<x<0.042. Large XMCD asymmetries at the L3 edge indicate significant
spin-polarization of the density of states at the Fermi energy. The spectral
shapes of the XAS and XMCD are nearly identical with those for Ga1-xMnxAs
indicating that the hybridization of Mn d states and anion p states is similar
in the two materials. Finally, compensation with sulfur donors not only lowers
the ferromagnetic Curie temperature but also reduces the spin polarization of
the hole states.Comment: 2 pages, 1 figure; To appear in the Proceedings of the 28th
International Conference on the Physics of Semiconductors (ICPS-28, Vienna,
Austria, July 24-28, 2006
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