pinecone/core-2020-05-10-deduplication huggingface dataset:
Light-induced degradation in copper-contaminated gallium-doped silicon

To date, gallium-doped Czochralski (Cz) silicon has constituted a solar cell bulk material free of light-induced degradation. However, we measure light-induced degradation in gallium-doped Cz silicon in the presence of copper impurities. The measured degradation depends on the copper concentration and the material resistivity. Gallium-doped Cz silicon is found to be less sensitive to copper impurities than borondoped Cz silicon, emphasizing the role of boron in the formation of copper-related light-induced degradation.Peer reviewe
Ultra-low acoustic-phonon-limited mobility and giant phonon-drag
  thermopower in MgZnO/ZnO heterostructures

We present numerical simulations of the acoustic-phonon-limited mobility,
$\mu_{ac}$, and phonon-drag thermopower, $S^{g}$, in two-dimensional electron
gases confined in MgZnO/ZnO heterostructures. The calculations are based on the
Boltzmann equation and are made for temperatures in the range 0.3-20 K and
sheet densities $0.5$-$30\times 10^{15}$ m$^{-2}$. The theoretical estimations
of $\mu_{ac}$ are in good agreement with the experiment without any adjustable
parameters. We find that the magnitude of $\mu_{ac}$ is dramatically decreased
in relation to GaAs based heterostructures. The phonon-drag thermopower,
$S^{g}$, which according to Herring's expression is inversely proportional to
$\mu_{ac}$ is severely increased exceeding 200 mV/K at $T=5$ K depending on
sheet density. The giant values of $S^{g}$ lead to a strong improvement of the
figure of merit $ZT$ at low temperatures. Our findings suggest that MgZnO/ZnO
heterostructures can be candidates for good thermoelectric materials at
cryogenic temperatures.Comment: 5 pages, 4 figure
Electronic comparison of InAs wurtzite and zincblende phases using
  nanowire transistors

We compare the electronic characteristics of nanowire field-effect
transistors made using single pure wurtzite and pure zincblende InAs nanowires
with nominally identical diameter. We compare the transfer characteristics and
field-effect mobility versus temperature for these devices to better understand
how differences in InAs phase govern the electronic properties of nanowire
transistors.Comment: Submitted to Physica Status Solidi - Rapid Research Letters Focus
  Issue on Semiconductor Nanowire
Spin textures of strongly correlated spin Hall quantum dots

We study the spin ordering of a quantum dot defined via magnetic barriers in
an interacting quantum spin Hall edge. The spin-resolved density-density
correlation functions are computed. We show that strong electron interactions
induce a ground state with a highly correlated spin pattern. The crossover from
the liquid-type correlations at weak interactions to the ground state spin
texture found at strong interactions parallels the formation of a
one-dimensional Wigner molecule in an ordinary strongly interacting quantum
dot.Comment: Accepted for publication on Physica Status Solidi - Rapid Research
  Letters (early view
Passivation of black silicon boron emitters with atomic layer deposited aluminum oxide

The nanostructured surface – also called black silicon (b-Si) – is a promising texture for solar cells because of its extremely low reflectance combined with low surface recombination obtained with atomic layer deposited (ALD) thin films. However, the challenges in keeping the excellent optical properties and passivation in further processing have not been addressed before. Here we study especially the applicability of the ALD passivation on highly boron doped emitters that is present in crystalline silicon solar cells. The results show that the nanostructured boron emitters can be passivated efficiently using ALD Al2O3 reaching emitter saturation current densities as low as 51 fA/cm2. Furthermore, reflectance values less than 0.5% after processing show that the different process steps are not detrimental for the low reflectance of b-Si.Peer reviewe
Strain engineering of topological properties in lead-salt semiconductors

Rock-salt chalcogenide SnTe represents the simplest realization of a
topological insulator where a crystal symmetry allows for the appearence of
topologically protected metallic states with an even number of Dirac cones on
high-symmetry crystal surfaces. Related rock-salt lead chalcogenides have been
predicted as well to undergo a phase-transition to a topological crystalline
insulating phase after band inversion induced by alloying and pressure. Here we
theoretically predict that strain, as realized in thin films grown on (001)
substrates, may induce such topological phase-transitions. Furthermore,
relevant topological properties of the surface states, such as the location of
the Dirac cones on the surface Brillouin zone or the decay length of edge
states, appear to be tunable with strain, with potential implications for
technological devices benefiting from those additional degrees of freedom
DFT and k * p modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells

Published online 30 october 2013. This work was performed using HPC resources from GENCI-CINES/IDRIS grant 2013-c2013096724.International audience3D hybrid organic perovskites, CH3NH3PbX3 (X = halogen), have recently been used to strongly improve the efficiency of dye sensitized solar cells (DSSC) leading to a new class of low-cost mesoscopic solar cells. CsSnI3 perovskite can also be used for hole conduction in DSSC. Density functional theory and GW corrections are used to compare lead and tin hybrid and all-inorganic perovskites. The room temperature optical absorption is associated to electronic transitions between the spin-orbit split-off band in the conduction band and the valence band. Spin-orbit coupling is about three times smaller for tin. Moreover, the effective mass of relevant band edge hole states is small (0.17). The high temperature phase sequence of CsSnI3 leading to the room temperature orthorhombic phase and the recently reported phases of CH3NH3MI3 (where M = Pb, Sn) close to the room temperature, are also studied. Tetragonal distortions from the ideal cubic phase are analysed by a k * p perturbation, including spin-orbit effect. In addition, the non-centrosymmetric phases of CH3NH3MI3 exhibit a splitting of the electronic bands away from the critical point. The present work shows that their physical properties are more similar to conventional semiconductors than to the absorbers used in DSS
Saturated Low-Temperature Conductivity in Ultrafast Semiconductor
  Nanocomposites

This article presents studies on low-field electrical conduction in the range
4-to-300 K for a ultrafast material: InGaAs:ErAs grown by molecular beam
epitaxy. The unique properties include nano-scale ErAs crystallines in host
semiconductor, a deep Fermi level, and picosecond ultrafast photocarrier
recombination. As the temperature drops, the conduction mechanisms are in the
sequence of thermal activation, nearest-neighbor hopping, variable-range
hopping, and Anderson localization. In the low-temperature limit,
finite-conductivity metallic behavior, not insulating, was observed. This
unusual conduction behavior is explained with the Abrahams scaling theory
Photoelectrochemical properties of texture-controlled nanostructured α-Fe2O3 thin films prepared by AACVD

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Nanostructured α-Fe2O3 thin film electrodes were deposited by aerosol-assisted chemical vapour deposition (AACVD) for photoelectrochemical (PEC) water splitting on conducting glass substrates using 0.1 M methanolic solution of Fe(acac)3. The XRD analysis confirmed that the films are highly crystalline α-Fe2O3 and free from other iron oxide phases. The highly reproducible electrodes have an optical bandgap of ~2.15 eV and exhibit anodic photocurrent. The current-voltage characterization of the electrodes reveals that the photocurrent density strongly depended on the film morphology and deposition temperature. Scanning electron microscopy (SEM) analysis showed a change in the surface morphology with the change in deposition temperature. The films deposited at 450 °C have nanoporous structures which provide a maximum electrode/electrolyte interface. The maximum photocurrent density of 455 μA/cm2 was achieved at 0.25 V vs. Ag/AgCl/3M KCl (~1.23 V vs. RHE) and the incident photon to electron conversion efficiency (IPCE) was 23.6% at 350 nm for the electrode deposited at 450 °C
High-mobility pentacene OTFT with TaLaO gate dielectric passivated by fluorine plasma

Pentacene thin-film transistor with high-κ TaLaO as gate dielectric has been fabricated and shows a carrier mobility of 0.73 cm2/V s, much higher than that based on pure La2O3 (0.43 cm2/V s) due to the smoother surface of the TaLaO film and thus larger pentacene islands grown on it in the initial stage. Moreover, among various times for fluorine-plasma treatment on the TaLaO gate dielectric, 100 seconds result in the highest carrier mobility of 1.12 cm2/V s due to (1) smoothest oxide surface achieved by fluorine passivation of oxide traps, as measured by AFM and supported by smallest sub-threshold swing and lowest low-frequency noise; (2) the largest pentacene grains grown on the smoothest oxide surface, as demonstrated by AFM.   Pentacene islands on on TaLaO or La2O3 gate dielectric with different plasma treatment times.postprin
Non-magnetic defects in the bulk of two-dimensional topological
  insulators

We found that non-magnetic defects in two-dimensional topological insulators
induce bound states of two kinds for each spin orientation: electron- and
hole-like states. Depending on the sign of the defect potential these states
can be also of two kinds with different distribution of the electron density.
The density has a maximum or minimum in the center. A surprising effect caused
by the topological order is a singular dependence of the bound-state energy on
the defect potential.Comment: 4 pages, 2 figures, to be published in Physica Status Solidi RR
Photoluminescence of focused ion beam implanted
  Er$^{3+}$:Y$_{2}$SiO$_{5}$ crystals

Erbium doped low symmetry Y$_2$SiO$_5$ crystals attract a lot of attention in
perspective of quantum information applications. However, only doping of the
samples during growth is available up to now, which yields a quite homogeneous
doping density. In the present work, we deposit Er$^{3+}$-ions by the focused
ion beam technique at Yttrium sites with several fluences in one sample. With a
photoluminescence study of these locally doped Er$^{3+}$:Y$_2$SiO$_5$ crystals,
we are able to evaluate the efficiency of the implantation process and develop
it for the highest efficiency possible. We observe the dependence of the ion
activation after the post-implantation annealing on the fluence value
Amorphous crystalline silicon heterojunction solar cells with black silicon texture

Excellent passivation of black silicon surfaces by thin amorphous silicon layers deposited  with plasma enhanced chemical vapor deposition is demonstrated. Minority charge carrier lifetimes of 1.3 milliseconds, enabling an implied open circuit voltage of 714 mV, were achieved. The influence of amorphous silicon parasitic epitaxial growth and thickness, as well as of the texture depth is investigated. Furthermore quantum efficiency gains for wavelenghts above 600 ,nm, as compared to random textured solar cells, are demonstrated in 17.2   efficient amorphous crystalline silicon heterojunction solar cells with black silicon textur
Fermi liquid breakdown and evidence for superconductivity in
  YFe$_2$Ge$_2$

In the d-electron system YFe$_2$Ge$_2$, an unusually high and temperature
dependent Sommerfeld ratio of the specific heat capacity $C/T \sim
100~\mathrm{mJ/(molK^2)}$ and an anomalous power law temperature dependence of
the electrical resistivity $\rho \simeq \rho_0 + AT^{3/2}$ signal Fermi liquid
breakdown, probably connected to a close-by quantum critical point. Full
resistive transitions, accompanied by DC diamagnetic screening fractions of up
to 80\% suggest that pure samples of YFe$_2$Ge$_2$ superconduct below
$1.8~\mathrm{K}$.Comment: 4 pages, 3 figures, published in Phys. Status Solidi RR
Engineered pixels using active plasmonic holograms with liquid crystals

Digital holography requires arrays of small reconfigurable elements to achieve complex reconstruction of the hologram with common systems based on pixels utilizing liquid crystal on silicon (LCoS) technology. The backplane of a typical pixel element is potentially underutilized and thus relatively large physical areas exist in which information can be stored and exploited to give additional functionality to pixel elements. Polarisation and wavelength dependent optical properties can be achieved in small areas using the plasmonic effects of optical antennae. The integration of LCs with optical antennae-based plasmonic holograms allows active modulation of the far field pattern. The work here demonstrates the concept that conventional LCoS pixel elements can be greatly enhanced with the integration of plasmonic holograms, composed of optical antennae patterned on the surface, giving rise to new levels of modulation capability for holographic pixel elements. Using LCs, polarisation dependent effects in plasmonic holograms can be switched. ‘Engineered pixels’, with sub-wavelength multiplexing over both polarisation and wavelength, can increase the channel capacity of a typical LC display device.CW would like to thank the EPSRC Integrated Photonic and Electronic Systems (IPES) Centre for Doctoral Training for their financial support. Y.M., J.O.T.-P, A.C.-V received financial sup-port from the Cambridge Overseas Trust and the Mexican National Council on Science and Technology.This is the final published version. It first appeared at http://onlinelibrary.wiley.com/doi/10.1002/pssr.201409524/abstract
Nanoimprint texturing of transparent flexible substrates for improved light management in thin-film solar cells

We present a nanoimprint based approach to achieve efficient light management for solar cells on low temperature transparent polymer films. These films are particularly low-priced, though sensitive to temperature, and therefore limiting the range of deposition temperatures of subsequent solar cell layers. By using nanoimprint technology, we successfully replicated optimized light trapping textures of etched high temperature ZnO:Al on a low temperature PET film without deterioration of optical properties of the substrate. The imprint-textured PET substrates show excellent light scattering properties and lead to significantly improved incoupling and trapping of light in the solar cell, resulting in a current density of 12.9 mA/cm2, similar to that on a glass substrate. An overall efficiency of 6.9% was achieved for a flexible thin-film silicon solar cell on low cost PET substrate
Micro-photoluminescence spectroscopy on heavily-doped layers of silicon solar cells

We report and explain the photoluminescence spectra emitted from silicon solar cells with heavily-doped layers at the surface. A micro-photoluminescence spectroscopy system is employed to investigate the total spectrum emitted from both the heavily-doped layer and the silicon substrate with micron-scale spatial resolution. The two regions of the device give rise to separate photoluminescence peaks, due to band-gap narrowing effects in the highly-doped layer. Two key parameters, the absorption depth of the excitation wavelength, and the sample temperature, are shown to be critical to reveal the separate signatures from the two regions. Finally, this technique is applied to locally diffused and laser-doped regions on silicon solar cell pre-cursors, demonstrating the potential value of this micron-scale technique in studying and optimizing locally doped regions.This work has been supported by the Australian Research Council (ARC) and the Australian Renew-able Energy Agency (ARENA) through research grant RND009
Graphene quantum dots probed by scanning tunneling spectroscopy and
  transport spectroscopy after local anodic oxidation

Graphene quantum dots are considered as promising alternatives to quantum
dots in III-V semiconductors, e.g., for the use as spin qubits due to their
consistency made of light atoms including spin-free nuclei which both imply
relatively long spin decoherene times. However, this potential has not been
realized in experiments so far, most likely, due to a missing control of the
edge configurations of the quantum dots. Thus, a more fundamental investigation
of Graphene quantum dots appears to be necessary including a full control of
the wave function properties most favorably during transport spectroscopy
measurements. Here, we review the recent success in mapping wave functions of
graphene quantum dots supported by metals, in particular Ir(111), and show how
the goal of probing such wave functions on insulating supports during transport
spectroscopy might be achieved.Comment: 14 pages, review articl
Sublattice engineering and voltage control of magnetism in triangular single and bi-layer graphene quantum dots

When a Dirac electron is confined to a triangular graphene quantum dot with zigzag edges, its low-energy spectrum collapses to a shell of degenerate states at the Fermi level leading to a magnetized edge. The shell degeneracy and the total magnetization are proportional to the edge size and can be made macroscopic. In this review, we start with a general discussion of magnetic properties of graphene structures and its relation to broken sublattice symmetry. Then, we discuss single electronic properties of single and bilayer triangular graphene quantum dots, focusing on the nature of edge states. Finally, we investigate the role of electronic correlations in determining the nature of ground state and excitation spectra of triangular graphene quantum dots as a function of dot size and filling fraction of the shell of zero-energy states. The interactions are treated by a combination of tight-binding, Hartree-Fock and configuration interaction methods. We show that the spin polarization of the triangular graphene quantum dots can be controlled through gating, i.e., by adding or removing electrons. In bilayer graphene dots, the relative filling of edge states in each layer and the magnetization can be tuned down to single localized spin using an external vertical electrical field.The Science Academy, Turkey, under the BAGEP program; TUBITAK, under the BIDEP program; NSERC; University of Ottawa; NRC Canada (IP2012 007372
Band gap and broken chirality in single-layer and bilayer graphene

Chirality is one of the key features governing the electronic properties of
single- and bilayer graphene: the basics of this concept and its consequences
on transport are presented in this review. By breaking the inversion symmetry,
a band gap can be opened in the band structures of both systems at the K-point.
This leads to interesting consequences for the pseudospin and, therefore, for
the chirality. These consequences can be accessed by investigating the
evolution of the Berry phase in such systems. Experimental observations of
Fabry-Perot interference in a dual-gated bilayer graphene device are finally
presented and are used to illustrate the role played by the band gap on the
evolution of the pseudospin. The presented results can be attributed to the
breaking of the chirality in the energy range close to the gap.Comment: To be published in Physica Status Solidi (RRL) - Rapid Research
  Letter
Spintronics with graphene quantum dots

Thanks to its intrinsic ability to preserve spin coherence, graphene is a
prime material for spintronics. In this review article, we summarize recent
achievements related to spintronics in graphene quantum dots and motivate this
field from a spintronics and a materials science point of view. We focus on
theory but also discuss recent experiments. The main sources of spin
decoherence are interactions with lattice excitations and the hyperfine
interaction with present nuclear spins. We explain effective spin-phonon
coupling in detail and present a generic power law for the spin relaxation time
T1 as a function of the magnetic field. For specific cases, we discuss spin
relaxation in detail. The Heisenberg exchange interaction is paramount for
coherent spin qubit operation and addressed in the context of magnetism in
graphene nano flakes. Nuclear spins in the host and surrounding material can be
considered by several means and the influence of 13C nuclei has been studied in
detail. Impressive advances in general spintronics and the fabrication of
graphene devices are likely to spark significant advances in spintronics with
graphene quantum dots in the near future.Comment: 15 pages, 1 abstract figure, 8 body figure
Identification of excitons, trions and biexcitons in single-layer WS2

Single-layer WS$_2$ is a direct-gap semiconductor showing strong excitonic
photoluminescence features in the visible spectral range. Here, we present
temperature-dependent photoluminescence measurements on mechanically exfoliated
single-layer WS$_2$, revealing the existence of neutral and charged excitons at
low temperatures as well as at room temperature. By applying a gate voltage, we
can electrically control the ratio of excitons and trions and assert a residual
n-type doping of our samples. At high excitation densities and low
temperatures, an additional peak at energies below the trion dominates the
photoluminescence, which we identify as biexciton emission.Comment: 6 pages, 5 figure
Observation of three-dimensional Dirac semimetal state in topological
  insulator Bi2Se3

The three dimensional (3D) topological insulators are predicted to exhibit a
3D Dirac semimetal state in critical regime of topological to trivial phase
transition. Here we demonstrate the first experimental evidence of 3D Dirac
semimetal state in topological insulator Bi2Se3 with bulk carrier concentration
of ~ 10^19 cm^{-3}, using magneto-transport measurements. At low temperatures,
the resistivity of our Bi2Se3 crystal exhibits clear Shubnikov-de Haas (SdH)
oscillations above 6T. The analysis of these oscillations through
Lifshitz-Onsanger and Lifshitz-Kosevich theory reveals a non-trivial pi Berry
phase coming from 3D bands, which is a decisive signature of 3D Dirac semimetal
state. The large value of Dingle temperature and natural selenium vacancies in
our crystal suggest that the observed 3D Dirac semimetal state is an outcome of
enhanced strain field and weaker effective spin-orbit coupling.Comment: 5 pages, 6 figures, This work has been presented at 8th India
  Singapore Symposium in Condensed Matter Physics Feb 25-Feb 27, 2015 at Indian
  Institute of Technology, Kanpur, Indi
Hybrid density functional study of optically active Er$^{3+}$ centers in
  GaN

Understanding the luminescence of GaN doped with erbium (Er) requires a
detailed knowledge of the interaction between the rare-earth dopant and the
nitride host, including intrinsic defects and other impurities that may be
present in the host material. We address this problem through a
first-principles hybrid density functional study of the structure, energetics,
and transition levels of the Er impurity and its complexes with N and Ga
vacancies, substitutional C and O impurities, and H interstitials in wurtzite
GaN. We find that, in the interior of the material, Er$_{\rm Ga}$ is the
dominant Er$^{3+}$ center with a formation energy of 1.55 eV; Er$_{\rm
Ga}$-$V_{\rm N}$ possesses a deep donor level at 0.61 eV which can assist in
the transfer of energy to the 4$f$-electron core. Multiple optically active
Er$^{3+}$ centers are possible in Er-doped GaN.Comment: 4 pages, 3 figures; minor changes. in Phys. Status Solidi RRL (2015