297 research outputs found
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
High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects
A large magnetoresistance effect is obtained at room-temperature by using
p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is
the virtual elimination of thermal currents due to the presence of band gaps in
the contacts. The current at B=0T is greatly decreased while the current at
B>0T is relatively large due to the band-to-band tunneling effects, resulting
in a high magnetoresistance ratio, even at room-temperature. Moreover, we
explore the effects of edge-roughness, length, and width of GNR channels on
device performance. An increase in edge-roughness and channel length enhances
the magnetoresistance ratio while increased channel width can reduce the
operating bias.Comment: http://dx.doi.org/10.1063/1.362445
Electric field induced charge injection or exhaustion in organic thin film transistor
The conductivity of organic semiconductors is measured {\it in-situ} and
continuously with a bottom contact configuration, as a function of film
thickness at various gate voltages. The depletion layer thickness can be
directly determined as a shift of the threshold thickness at which electric
current began to flow. The {\it in-situ} and continuous measurement can also
determine qualitatively the accumulation layer thickness together with the
distribution function of injected carriers. The accumulation layer thickness is
a few mono layers, and it does not depend on gate voltages, rather depends on
the chemical species.Comment: 4 figures, to be published in Phys. Rev.
Selective Dynamic Nuclear Spin Polarization in Spin-Blocked Double-Dot
We study the mechanism of dynamical nuclear spin polarization by hyperfine
interaction in spin-blocked double quantum dot system. We calculate the
hyperfine transition rates and solve the master equations for the nuclear
spins. Specifically, we incorporate the effects of the nuclear quadrupole
coupling due to the doping-induced local lattice distortion and strain. Our
results show that nuclear quadrupole coupling induced by the 5% indium
substitution can be used to explain the recent experimental observation of
missing arsenic NMR signal in the spin-blocked double dots.Comment: 4 pages, 3 figure
Absence of an intrinsic value for the surface recombination velocity in doped semiconductors
A self-consistent expression for the surface recombination velocity and
the surface Fermi level unpinning energy as a function of light excitation
power () is presented for n- and p-type semiconductors doped above the
10 cm range. Measurements of on p-type GaAs films using a
novel polarized microluminescence technique are used to illustrate two limiting
cases of the model. For a naturally oxidized surface is described by a
power law in whereas for a passivated surface varies
logarithmically with . Furthermore, the variation in with surface state
density and bulk doping level is found to be the result of Fermi level
unpinning rather than a change in the intrinsic surface recombination velocity.
It is concluded that depends on throughout the experimentally
accessible range of excitation powers and therefore that no instrinsic value
can be determined. Previously reported values of on a range of
semiconducting materials are thus only valid for a specific excitation power.Comment: 10 pages, 7 figure
Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy
Deep level defects in n-type unintentionally doped a-plane MgxZn1−xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1−xO were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of Ec − 1.4 eV, 2.1 eV, 2.6 V, and Ev + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at Ec − 2.1 eV, Ev + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at Ev + 0.3 eV and Ec − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the Ev + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the Ec − 1.4 eV and Ec − 2.6 eV levels in Mg alloyed samples
Temperature dependent transport characteristics of graphene/n-Si diodes
Realizing an optimal Schottky interface of graphene on Si is challenging, as
the electrical transport strongly depends on the graphene quality and the
fabrication processes. Such interfaces are of increasing research interest for
integration in diverse electronic devices as they are thermally and chemically
stable in all environments, unlike standard metal/semiconductor interfaces. We
fabricate such interfaces with n-type Si at ambient conditions and find their
electrical characteristics to be highly rectifying, with minimal reverse
leakage current (10 A) and rectification of more than . We
extract Schottky barrier height of 0.69 eV for the exfoliated graphene and 0.83
eV for the CVD graphene devices at room temperature. The temperature dependent
electrical characteristics suggest the influence of inhomogeneities at the
graphene/n-Si interface. A quantitative analysis of the inhomogeneity in
Schottky barrier heights is presented using the potential fluctuation model
proposed by Werner and G\"{u}ttler.Comment: 5 pages, 5 figure
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
Characterization of the Schottky Barrier in SrRuO3/Nb:SrTiO3 Junctions
Internal photoemission spectroscopy was used to determine the Schottky
barrier height in rectifying SrRuO3/Nb-doped SrTiO3 junctions for 0.01 wt % and
0.5 wt % Nb concentrations. Good agreement was obtained with the barrier height
deduced from capacitance-voltage measurements, provided that a model of the
nonlinear permittivity of SrTiO3 was incorporated in extrapolating the built-in
potential, particularly for high Nb concentrations. Given the generic
polarizability of perovskites under internal/external electric fields, internal
photoemission provides a valuable independent probe of the interface electronic
structure.Comment: 15 pages, 3 figure
Magnetodielectric Coupling in Nonmagnetic Au/GaAs:Si Schottky Barriers
We report on a heretofore unnoted giant negative magnetocapacitance (>20%) in
non-magnetic Au/GaAs:Si Schottky barriers that we attribute to a magnetic field
in-duced increase in the binding energy of the shallow donor Si impurity atoms.
Depletion capacitance (Cdep) dispersion identifies the impurity ionization and
capture processes that give rise to a magnetic field dependent density of
ionized impurities. Internal photoemission experiments confirm that the large
field-induced shifts in the built-in potential, inferred from 1/Cdep^2 vs
voltage measurements, are not due to a field-dependent Schottky barrier height,
thus requiring a modification of the abrupt junction approximation that
accounts for the observed magnetodielectric coupling.Comment: 25 pages, 5 figures, submitted to Phys. Rev.
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