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DOI: 10.4028/www.scientific.net/MSF.615-617.203
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We report a comparative investigation of Few layers graphene grown on 6H, 4H, and 3C-SiC substrates. We show that the size of the graphitic domains depends more on the < 0001 > SiC Surface orientation than the polytypism.

Commentaires: 7th European Conference on Silicon Carbide and Related Materials, Barcelona, SPAIN, SEP 07-11, 2008

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We report a comparative investigation of Few layers graphene grown on 6H, 4H, and 3C-SiC substrates. We show that the size of the graphitic domains depends more on the < 0001 > SiC Surface orientation than the polytypism.

Ref HAL: hal-00543293_v1
DOI: 10.1103/PhysRevB.80.033304
WoS: 000268617800018
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9 Citations
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We performed a local spectroscopy of the Landau levels density of states using gated mesoscopic Hall bars placed at very low temperature in the integer quantum Hall regime. The transverse and longitudinal conductances were measured while scanning both the two-dimensional electron density and the applied magnetic field. We observe a succession of sharp peaks due to backscattering across the samples caused by tunneling effects. Using temperature as a parameter in the range of 0.1-1 K, we characterize those tunnel processes: a resonant double-barrier tunneling and a single-barrier tunneling which corresponds to the variable range hopping regime. We show that for vanishing temperature and noninteger filling factor nu the conductance sigma(T=0, nu) does not vanish unlike the case of wide samples: instead, it converges to a limit function sigma(S)(nu) that is a noisy image of the Landau levels density of states.

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Samples consisting of a few layers of graphene obtained by thermal decomposition of SiC were studied by means of transport experiments at 4 K and in a magnetic field up to 7 T. Transport data show that the samples have a two-dimensional character. Magnetoresistance has an approximately linear character at high magnetic fields, which has been previously observed in graphite samples, and a negative magnetoresistance, at low magnetic fields. The transverse resistivity rho(xy) is nonlinear as a function of B, which can be described using a many-carrier model

Ref HAL: hal-00439962_v1
DOI: 10.1103/PhysRevB.79.041307
WoS: 000262978400009
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10 Citations
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The Zeeman splittings of a Si shallow donor in AlAs and of a two-dimensional electron gas (2DEG) in GaAs are evidenced by resonant tunneling spectroscopy in submicrometer GaAs/AlAs/GaAs junctions. In magnetic field, the donor acts as a spin-sensitive probe of the spin-polarized density of states in the emitter. In the current-voltage characteristic the two splittings are resolved, which allows us to estimate the Landé g factors for the impurity gI=+1.96±0.16 and for the 2DEG. Because of spin conservation in the tunneling between the 2DEG and the donor, the relative sign of the two g factors can be determined.

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We present a detailed investigation of the different factors that rule the temperature dependence of the AlGaN/AlN/GaN Hall-FET devices in the temperature range 300-500 degrees C. To understand the origin of the apparent increase in drive-in current density which affects devices above 300 degrees C, several series of experiments have been done. We checked: (i) the constitutive materials resistance to elevated temperature, (ii) the insulation of the buffer layer, (iii) the stability of the carrier density in the two-dimensional electron gas and, finally, (iv) the performance of devices after temperature cycling. We found that, both, the material properties and insulation of the buffer layers remains satisfactory up to 500 degrees C. The carrier density remains also very stable. However, we observe some material deterioration after temperature cycling which suggests that, in such non-passivated devices, the thermal drift could be due to partial deterioration of the surface layers and/or the gate Schottky contact. (C) 2008 Elsevier B.V. All rights reserved.

Ref HAL: hal-00394184_v1
DOI: 10.1063/1.3103303
WoS: 000266633500090
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3 Citations
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The Hall resistance of small Hall sensors and its nonlinear dependence on magnetic field B were investigated at the temperature of 4.2 K. The sensors were four-terminal crosses fabricated by etching AlGaAs/InGaAs/GaAs delta-doped heterostructures. While large sensors exhibit good linearity of the Hall voltage on magnetic field, in sensors smaller than 5 mu m we detected pronounced nonlinearities for magnetic fields between 0 and 2 T. We attribute the latter to ballistic corrections to the classical Hall effect, and we model the Hall and the bend resistances at low temperature using Monte Carlo simulation. We also carried out temperature studies of the Hall sensors. We show that the nonlinearities persist up to room temperature. The effect of nonlinearities on the performance of Hall sensors is discussed.