13 research outputs found
The Rashba Hamiltonian and electron transport
The Rashba Hamiltonian describes the splitting of the conduction band as a
result of spin-orbit coupling in the presence of an external field and is
commonly used to model the electronic structure of confined narrow-gap
semiconductors. Due to the mixing of spin states some care has to be exercised
in the calculation of transport properties. We derive the velocity operator for
the Rashba-split conduction band and demonstrate that the transmission of an
interface between a ferromagnet and a Rashba-split semiconductor does not
depend on the magnetization direction, in contrast with previous assertions in
the literature.Comment: one tex file, two figures; paper to appear in this form in PRB (RC
Magnetotunneling Between Two-dimensional Electron Gases in InAs-AlSb-GaSb Heterostructures
We have observed that the tunneling magnetoconductance between
two-dimensional (2D) electron gases formed at nominally identical InAs-AlSb
interfaces most often exhibits two sets of Shubnikov-de Haas oscillations with
almost the same frequency. This result is explained quantitatively with a model
of the conductance in which the 2D gases have different densities and can
tunnel between Landau levels with different quantum indices. When the epitaxial
growth conditions of the interfaces are optimized, the zero-bias
magnetoconductance shows a single set of oscillations, thus proving that the
asymmetry between the two electron gases can be eliminated.Comment: RevTeX format including 4 figures; submit for publicatio
Radiation-induced oscillatory magnetoresistance as a sensitive probe of the zero-field spin splitting in high mobility GaAs/AlGaAs devices
We suggest an approach for characterizing the zero-field spin splitting of
high mobility two-dimensional electron systems, when beats are not readily
observable in the Shubnikov-de Haas effect. The zero-field spin splitting and
the effective magnetic field seen in the reference frame of the electron is
evaluated from a quantitative study of beats observed in radiation-induced
magnetoresistance oscillations.Comment: 4 pages, 4 color figure
Spin transport of electrons through quantum wires with spatially-modulated strength of the Rashba spin-orbit interaction
We study ballistic transport of spin-polarized electrons through quantum
wires in which the strength of the Rashba spin-orbit interaction (SOI) is
spatially modulated. Subband mixing, due to SOI, between the two lowest
subbands is taken into account. Simplified approximate expressions for the
transmission are obtained for electron energies close to the bottom of the
first subband and near the value for which anticrossing of the two lowest
subbands occurs. In structures with periodically varied SOI strength, {\it
square-wave} modulation on the spin transmission is found when only one subband
is occupied and its possible application to the spin transistor is discussed.
When two subbands are occupied the transmission is strongly affected by the
existence of SOI interfaces as well as by the subband mixing
Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions
Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagnetic
junctions is studied theoretically within the Landauer framework of ballistic
transport. We show that quantum coherence can have unexpected implications for
spin injection and that some intuitive spintronic concepts which are founded in
semi-classical physics no longer apply: A quantum spin-valve (QSV) effect
occurs even in the absence of a net spin polarized current flowing through the
device, unlike in the classical regime. The converse effect also arises, i.e. a
zero spin-valve signal for a non-vanishing spin-current. We introduce new
criteria useful for analyzing quantum and classical spin transport phenomena
and the relationships between them. The effects on QSV behavior of
spin-dependent electron transmission at the interfaces, interface Schottky
barriers, Rashba spin-orbit coupling and temperature, are systematically
investigated. While the signature of the QSV is found to be sensitive to
temperature, interestingly, that of its converse is not. We argue that the QSV
phenomenon can have important implications for the interpretation of
spin-injection in quantum spintronic experiments with spin-valve geometries.Comment: 15 pages including 11 figures. To appear in PR
High-GF planar aluminium-silicon hybrid strain transducers
We demonstrate here a simple planar aluminium-silicon strain sensor incorporating an external aluminium ohmic shunt (metal-semiconductor hybrid) which exhibits a geometrically enhanced room-temperature gauge factor (GF) of up to 843 under uni-axial tensile strains of up of 8 times 10 -5 for a silicon p-type doping level of 1 times 10 17 cm -3 . We also show that the GF is dependent on the silicon doping density; a GF of 317 being demonstrated for a p-type doping density of 1 times 10 20 cm -3 . Moreover a GF well above 1000 is possible in more lightly doped samples. The observed behaviour, to be contrasted with the gauge factor of -93 observed in homogeneous p-type silicon, is the result of the stress-induced anisotropy in the silicon conductivity that acts to deflect the current away from the metallic shunt for tensile strains
Piezoresistance in Silicon at Uniaxial Compressive Stresses up to 3 GPa
The room-temperature longitudinal piezoresistance of n-type and p-type crystalline silicon along selected crystal axes is investigated under uniaxial compressive stresses up to 3 GPa. While the conductance (G) of n-type silicon eventually saturates at about 45% of its zero-stress value (G0) in accordance with the charge transfer model, in p-type material G=G0 increases above a predicted limit of about 4.5 without any significant saturation, even at 3 GPa. Calculation of G=G0 using ab initio density functional theory reveals that neither G nor the mobility, when properly averaged over the hole distribution, saturate at stresses lower than 3 GPa. The lack of saturation has important consequences for strained-silicon technologies
Giant, Anomalous Piezoimpedance in Silicon-on-insulator
International audienceA giant, anomalous piezoresponse of fully depleted silicon-on-insulator devices under mechanical stress is demonstrated by impedance spectroscopy. This piezoresponse strongly depends on the measurement frequency, ω, and consists of both a piezoresistance (PZR) and a piezocapacitance, whose maximum values are −1100 × 10−11 and −900 × 10−11 Pa−1, respectively. These values should be compared withthe usual bulk PZR in p-type silicon, 70 × 10−11 Pa−1. The observations are well described by models of space-charge-limited hole currents in the presence of fast electronic traps having stress-dependent capture rates (ωc) and emission rates. Under steady-state conditions (i.e., when ω ωc), where the impedancespectroscopy measurements yield results that are directly comparable with those of previously published reports of PZR in depleted, silicon nano-objects, the overall piezoresponse is just the usual, bulk silicon PZR. Anomalous PZR is observed only under non-steady-state conditions when ω ≈ ωc, with a symmetry suggesting that the electromechanically active fast traps are native Pb0 interface defects. The observations suggest new functionalities for fully depleted silicon-on-insulator, and shed light on the debate over the PZR of carrier-depleted nanosilicon
Mechanical stress dependence of the Fermi level pinning on an oxidized silicon surface
International audienceA combination of micro-Raman spectroscopy and micro-XPS (X-ray photo-electron spectroscopy) mapping on statically deflected p-type silicon cantilevers is used to study the mechanical stress dependence of the Fermi level pinning at an oxidized silicon (001) surface. With uniaxial compressive and tensile stress applied parallel to the ⟨110⟩ crystal direction, the observations are relevant to the electronic properties of strain-silicon nano-devices with large surface-to-volume ratios such as nanowires and nanomembranes. The surface Fermi level pinning is found to be even in applied stress, a fact that may be related to the symmetry of the Pb0 silicon/oxide interface defects. For stresses up to 240 MPa, an increase in the pinning energy of 0.16 meV/MPa is observed for compressive stress, while for tensile stress it increases by 0.11 meV/MPa. Using the bulk, valence band deformation potentials the reduction in surface band bending in compression (0.09 meV/MPa) and in tension (0.13 meV/MPa) can be estimated