2,457 research outputs found
Graphite based Schottky diodes formed on Si, GaAs and 4H-SiC substrates
We demonstrate the formation of semimetal graphite/semiconductor Schottky
barriers where the semiconductor is either silicon (Si), gallium arsenide
(GaAs) or 4H-silicon carbide (4H-SiC). Near room temperature, the forward-bias
diode characteristics are well described by thermionic emission, and the
extracted barrier heights, which are confirmed by capacitance voltage
measurements, roughly follow the Schottky-Mott relation. Since the outermost
layer of the graphite electrode is a single graphene sheet, we expect that
graphene/semiconductor barriers will manifest similar behavior.Comment: 5 pages, 3 figures, 1 tabl
Superconducting Quantum Point contacts and Maxwell Potential
The quantization of the current in a superconducting quantum point contact is
reviewed and the critical current is discussed at different temperatures
depending on the carrier concentration as well by suggesting a constant
potential in the semiconductor and then a Maxwell potential. When the Fermi
wave length is comparable with the constriction width we showed that the
critical current has a step-like variation as a function of the constriction
width and the carrier concentration.Comment: 13 pages, 8 figures, some figures are clarified; scheduled to appear
in an issue in MPLB Vo.21, (2007
Hole mobility in organic single crystals measured by a "flip-crystal" field-effect technique
We report on single crystal high mobility organic field-effect transistors
(OFETs) prepared on prefabricated substrates using a "flip-crystal" approach.
This method minimizes crystal handling and avoids direct processing of the
crystal that may degrade the FET electrical characteristics. A chemical
treatment process for the substrate ensures a reproducible device quality. With
limited purification of the starting materials, hole mobilities of 10.7, 1.3,
and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single
crystals, respectively. Four-terminal measurements allow for the extraction of
the "intrinsic" transistor channel resistance and the parasitic series contact
resistances. The technique employed in this study shows potential as a general
method for studying charge transport in field-accumulated carrier channels near
the surface of organic single crystals.Comment: 26 pages, 7 figure
Spin-wave softening and Hund's coupling in ferromagnetic manganites
Using one-orbital model of hole-doped manganites, we show with the help of
Holstein-Primakov transformation that finite Hund's coupling is responsible for
the spin-wave softening in the ferromagnetic -phase manganites. We obtain an
analytical result for the spin-wave spectrum for \JH\gg t. In the limit of
infinte Hund's coupling, the spectrum is the conventional nearest-neighbor
Heisenberg ferromagnetic spin-wave. The o(t/\JH)-order correction is negative
and thus accounts for the softening near the zone boundary.Comment: 5 pages, 3 figure
Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers
We have investigated the size effect in lead zirconate titanate (PZT) thin
films with a range of manganese (Mn) doping concentrations. We found that the
size effect in the conventional Pt/PZT/Pt thin-film capacitors could be
systematically reduced and almost completely eliminated by increasing Mn doping
concentration. The interfacial layer at the electrode-film interface appears to
disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed
by the fits using the conventional in-series capacitor model. Our work
indicates that the size effect in ferroelectrics is extrinsic in nature,
supporting the work by Saad et al. Other implications of our results have also
been discussed. By comparing a variety of experimental studies in the
literature we propose a scenario that the dead layer between PZT (or barium
strontium titanate, BST) and metal electrodes such as Pt and Au might have a
defective pyrochlore/fluorite structure (possibly with a small portion of
ferroelectric perovskite phase).Comment: 21 pages, 6 figure
Unification of bulk and interface electroresistive switching in oxide systems
We demonstrate that the physical mechanism behind electroresistive switching
in oxide Schottky systems is electroformation, as in insulating oxides.
Negative resistance shown by the hysteretic current-voltage curves proves that
impact ionization is at the origin of the switching. Analyses of the
capacitance-voltage and conductance-voltage curves through a simple model show
that an atomic rearrangement is involved in the process. Switching in these
systems is a bulk effect, not strictly confined at the interface but at the
charge space region.Comment: 4 pages, 3 figures, accepted in PR
Quantitative analysis of electronic transport through weakly-coupled metal/organic interfaces
Using single-crystal transistors, we have performed a systematic experimental
study of electronic transport through oxidized copper/rubrene interfaces as a
function of temperature and bias. We find that the measurements can be
reproduced quantitatively in terms of the thermionic emission theory for
Schottky diodes, if the effect of the bias-induced barrier lowering is
included. Our analysis emphasizes the role of the coupling between metal and
molecules, which in our devices is weak due to the presence of an oxide layer
at the surface of the copper electrodes.Comment: 4 pages, 3 figure
Thermionic charge transport in CMOS nano-transistors
We report on DC and microwave electrical transport measurements in
silicon-on-insulator CMOS nano-transistors at low and room temperature. At low
source-drain voltage, the DC current and RF response show signs of conductance
quantization. We attribute this to Coulomb blockade resulting from barriers
formed at the spacer-gate interfaces. We show that at high bias transport
occurs thermionically over the highest barrier: Transconductance traces
obtained from microwave scattering-parameter measurements at liquid helium and
room temperature is accurately fitted by a thermionic model. From the fits we
deduce the ratio of gate capacitance and quantum capacitance, as well as the
electron temperature
Incoherent Transport through Molecules on Silicon in the vicinity of a Dangling Bond
We theoretically study the effect of a localized unpaired dangling bond (DB)
on occupied molecular orbital conduction through a styrene molecule bonded to a
n++ H:Si(001)-(2x1) surface. For molecules relatively far from the DB, we find
good agreement with the reported experiment using a model that accounts for the
electrostatic contribution of the DB, provided we include some dephasing due to
low lying phonon modes. However, for molecules within 10 angstrom to the DB, we
have to include electronic contribution as well along with higher dephasing to
explain the transport features.Comment: 9 pages, 5 figure
Anomalous change in leakage and displacement currents after electrical poling on lead-free ferroelectric ceramics
We report the polarization, displacement current and leakage current behavior
of a trivalent nonpolar cation Al cation substituted lead free ferroelectric
NBT-BT electroceramics with tetragonal phase and P4mm space group symmetry.
Nearly three orders of magnitude decrease in leakage current were observed
under electrical poling, which significantly improves microstructure,
polarization, and displacement current. Effective poling neutralizes the domain
pinning, traps charges at grain boundaries and fills oxygen vacancies with free
charge carriers in matrix, thus saturated macroscopic polarization in contrast
to that in upoled samples. E-poling changes bananas type polarization loops to
real ferroelectric loops.Comment: 18 pages, 5 figure
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