Ref HAL: hal-01203222_v1
DOI: 10.1103/PhysRevB.91.214111
WoS: 000356657200001
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4 Citations
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Branded for its potential electronic ferroelectricity, charge-ordered LuFe2O4 has a layered Fe triangular framework, whose topology is a source of degeneracy, both at the charge and spin levels. Here we present an in-depth characterization of LuFe2O4-hp, the high-pressure (hp) polymorph of LuFe2O4, using electron, x-ray, and neutron diffraction, combined with transport and magnetization measurements. We show that LuFe2O4-hp is characterized by a misfit-related monoclinic structure, accommodating a buckled triangular [Lu](infinity) layer and two shifted adjacent rectangular [Fe](infinity) planes belonging to a distorted rock salt-type layer. The release of the geometric frustration of the Fe magnetic lattice in the hp form leads to collinear antiferromagnetic ordering at T-N = 380 K. Possible coexistence of charge and magnetic orders in this material opens research pathways for the design of tunable multifunctional devices using high-pressure techniques.

Résumé:

Electron concentration and resistivity in n-GaN at high temperatures up to 1000 K

Ref HAL: hal-01936833_v1
DOI: 10.1002/pssb.201200508
WoS: 000318791900017
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1 Citation
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Pressure studies of multicarrier conduction in undoped InN grown on GaN buffer

Ref HAL: hal-01208523_v1
DOI: 10.1063/1.4813220
WoS: WOS:000321761600027
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We report magnetotransport measurements performed on AlGaN/GaN devices with different buffer layers. Standard samples with a 1 μm thick GaN buffer show a linear Hall resistance and an almost constant magnetoresistance, as expected from a single two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. Other samples, with an Al x Ga1– x N buffer (x = 5%) and a buried linear aluminium gradient, have an additional three-dimensional electron slab (3DES) close to the GaN substrate. In this case, the Hall resistance is strongly non-linear and presents an incorrect hole-type carrier signature, evidenced by low field mobility spectrum analysis. This effect is strengthened when the 3D layer, parallel to the mesa-etched 2DEG, is infinite. We suggest that the misplacement of the electrical contacts in the 3DES, i.e., far from the sample edges, could explain the wrong carrier type determination.

Commentaires: The authors would like to thank Dr. E. Litwin-Staszewska from the Institute of High Pressure Physics “Unipress,” for the Hall bar processing on the 3D electron slab. This work was supported by the GANEX program (ANR-11-LabEx-0014).

Ref HAL: hal-00803766_v1
DOI: 10.4028/www.scientific.net/MSF.740-742.357
WoS: 000319785500083
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2 Citations
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Raman scattering spectra have been collected on p-type 4H-SiC samples doped with aluminum up to 5×10^19 atoms per cubic cm. The distortion and asymmetry of FTA modes which appear in the low frequency range has been probed in great details. We show that, using standard Fano formulae with three parameters per mode, one can successively fit all FTA modes profiles in the concentration range 2×10^16 - 5×10^19 Al.cm-3

Ref HAL: hal-00807551_v1
DOI: 10.1016/j.jcrysgro.2011.12.021
WoS: 000304457800011
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15 Citations
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Crystallization of GaN by High Nitrogen Pressure Solution method in multi-feed-seed (MFS) configuration without intentional doping results in:(1) Growth of strongly n-type crystals with free electron concentration increasing with growth temperature in ranges of 2-6x1019 cm-3 and 1350-1430 °C, (2) stable growth on Ga-polar surface and unstable growth on N-pola rsurface ,crystals slightly brown, (3) improvement of (0001) crystallographic planes curvature (flattening) with respect to bowing oft hese planes in the seed crystals. The addition of magnesium into the growth solution causes strong compensation of freeelectrons in the crystals. Therefore, highly resistive GaN crystals can be grown. In this work, the crystallization of Mg doped GaN on flat 1 in. seeds (substrates) grown by HVPE in MFS configuration has been studied.

Ref HAL: hal-00806216_v1
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We present magneto-transport measurements performed on three AlGaN/AlN/GaN heterostructures up to 14 T for various temperatures in the range 4-300 K. The obtained longitudinal and Hall conductivities are processed by mobility spectrum algorithms in order to extract the number and type of carriers in the samples. A single carrier is found in the whole structure in agreement with the first subband occupancy of the triangular quantum well which forms at the AlN/GaN interface. The temperature dependences of the density and mobility of the two dimensional electron gas are plotted for all three samples and compared with respect to their layer structures.