3,407 research outputs found
Detection of a single-charge defect in a metal-oxide-semiconductor structure using vertically coupled Al and Si single-electron transistors
An Al-AlO_x-Al single-electron transistor (SET) acting as the gate of a
narrow (~ 100 nm) metal-oxide-semiconductor field-effect transistor (MOSFET)
can induce a vertically aligned Si SET at the Si/SiO_2 interface near the
MOSFET channel conductance threshold. By using such a vertically coupled Al and
Si SET system, we have detected a single-charge defect which is tunnel-coupled
to the Si SET. By solving a simple electrostatic model, the fractions of each
coupling capacitance associated with the defect are extracted. The results
reveal that the defect is not a large puddle or metal island, but its size is
rather small, corresponding to a sphere with a radius less than 1 nm. The small
size of the defect suggests it is most likely a single-charge trap at the
Si/SiO_2 interface. Based on the ratios of the coupling capacitances, the
interface trap is estimated to be about 20 nm away from the Si SET.Comment: 5 pages and 5 figure
Nanostructured electrodes for thermionic and thermo-tunneling devices
Recently, new quantum features have been studied in the area of ridged
quantum wells (RQW). Periodic ridges on the surface of the quantum well layer
impose additional boundary conditions on the electron wave function and reduce
the quantum state density. Electrons, rejected from forbidden quantum states,
have to occupy the states with higher energy. As a result, Fermi energy in RQW
increases and work function (WF) decreases. We investigate low WF electrode,
com-posed from a metal RQW layer and a base substrate. The substrate material
was selected so that electrons were confined to the RQW. The WF value depends
on ridge geometry and electron confinement. We calculate WF in the metal RQW
films grown both on a semiconductor and metal substrates. In the case of
semiconductor substrate, wide band gap materials are preferable as they allow
more reduction in RQW work function. In the case of metal substrate, low Fermi
energy materials are preferable. For most material pairs, the WF was reduced
dramatically. Such structures, can serve as electrodes for room temperature
thermionic and thermotunnel energy converters and coolers.Comment: 8 pages, 5 figures, 2 table
Heterostructure unipolar spin transistors
We extend the analogy between charge-based bipolar semiconductor electronics
and spin-based unipolar electronics by considering unipolar spin transistors
with different equilibrium spin splittings in the emitter, base, and collector.
The current of base majority spin electrons to the collector limits the
performance of ``homojunction'' unipolar spin transistors, in which the
emitter, base, and collector all are made from the same magnetic material. This
current is very similar in origin to the current of base majority carriers to
the emitter in homojunction bipolar junction transistors. The current in
bipolar junction transistors can be reduced or nearly eliminated through the
use of a wide band gap emitter. We find that the choice of a collector material
with a larger equilibrium spin splitting than the base will similarly improve
the device performance of a unipolar spin transistor. We also find that a
graded variation in the base spin splitting introduces an effective drift field
that accelerates minority carriers through the base towards the collector.Comment: 9 pages, 2 figure
Electrical transport across Au/Nb:SrTiO3 Schottky interface with different Nb doping
We have investigated electron transport in Nb doped SrTiO single crystals
for two doping densities. We find that the resistivity and mobility are
temperature dependent in both whereas the carrier concentration is almost
temperature invariant. We rationalize this using the hydrogenic theory for
shallow donors. Further, we probe electrical transport across Schottky
interfaces of Au on TiO terminated n-type SrTiO. Quantitative analysis
of macroscopic I-V measurements reveal thermionic emission dominated transport
for the low doped substrate whereas it deviates from such behavior for the high
doped substrate. This work is relevant for designing devices to study
electronic transport using oxide-semiconductors.Comment: 10 Pages, 3 Figure
Weak Localization and Antilocalization in Topological Insulator Thin Films with Coherent Bulk-Surface Coupling
We evaluate quantum corrections to conductivity in an electrically gated thin
film of a three-dimensional (3D) topological insulator (TI). We derive
approximate analytical expressions for the low-field magnetoresistance as a
function of bulk doping and bulk-surface tunneling rate. Our results reveal
parameter regimes for both weak localization and weak antilocalization, and
include diffusive Weyl semimetals as a special case.Comment: After publication, we have noticed and corrected two small but
potentially misleading typographic errors in Eqs. (2.27) and (2.29), where
the definitions of \tau_s and \tau_v were mistakenly switched. Once these
typographic errors are fixed, all the results remain unchanged. An Erratum
will be published in PR
Terahertz photoresponse of a quantum Hall edge-channel diode
The Teraherz (THz) photoresponse of a two-dimensional electron gas in the
quantum Hall regime is investigated. We use a sample structure which is
topologically equivalent to a Corbino geometry combined with a cross-gate
technique. This quasi-Corbino geometry allows us to directly investigate the
THz-induced transport between adjacent edge-states, thus avoiding bulk effects.
We find a pronounced photo voltage at zero applied bias, which rapidly
decreases when an external current bias is applied. The photo voltage and its
dependence on the bias current can be described using the model of an
illuminated photodiode, resulting from the reconstruction of the Landau bands
at the sample edge. Using the sample as a detector in a Fourier transform
spectrometer setup, we find a resonant response from which we extract a reduced
effective cyclotron mass. The findings support a non-bolometric mechanism of
the induced photo voltage and the proposed edge-channel diode model.Comment: 5 pages, 5 eps-figures, accepted for Phys. Rev.
Temperature Dependent Polarity Reversal in Au/Nb:SrTiO3 Schottky Junctions
We have observed temperature-dependent reversal of the rectifying polarity in
Au/Nb:SrTiO3 Schottky junctions. By simulating current-voltage characteristics
we have found that the permittivity of SrTiO3 near the interface exhibits
temperature dependence opposite to that observed in the bulk, significantly
reducing the barrier width. At low temperature, tunneling current dominates the
junction transport due both to such barrier narrowing and to suppressed thermal
excitations. The present results demonstrate that novel junction properties can
be induced by the interface permittivity
Impact of elasticity on the piezoresponse of adjacent ferroelectric domains investigated by scanning force microscopy
As a consequence of elasticity, mechanical deformations of crystals occur on
a length scale comparable to their thickness. This is exemplified by applying a
homogeneous electric field to a multi-domain ferroelectric crystal: as one
domain is expanding the adjacent ones are contracting, leading to clamping at
the domain boundaries. The piezomechanically driven surface corrugation of
micron-sized domain patterns in thick crystals using large-area top electrodes
is thus drastically suppressed, barely accessible by means of piezoresponse
force microscopy
Dielectric and polarization experiments in high loss dielectrics: a word of caution
The recent quest for improved functional materials like high permittivity
dielectrics and/or multiferroics has triggered an intense wave of research.
Many materials have been checked for their dielectric permittivity or their
polarization state. In this report, we call for caution when samples are
simultaneously displaying insulating behavior and defect-related conductivity.
Many oxides containing mixed valent cations or oxygen vacancies fall in this
category. In such cases, most of standard experiments may result in effective
high dielectric permittivity which cannot be related to ferroelectric
polarization. Here we list few examples of possible discrepancies between
measured parameters and their expected microscopic origin
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