285 research outputs found
Thermopower modulation clarification of the intrinsic effective mass in a transparent oxide semiconductor, BaSnO3
Although there are so many reports on the carrier effective mass (m*) of a
transparent oxide semiconductor BaSnO3, it is almost impossible to know the
intrinsic m* value because the reported m* values are scattered from 0.06 to
3.7 m0. Here we successfully clarified the intrinsic m* of BaSnO3, m*=0.40 0.01
m0, by the thermopower modulation clarification method. We also found the
threshold of degenerate/non-degenerate semiconductor of BaSnO3; At the
threshold, the thermopower value of both La-doped BaSnO3 and BaSnO3 TFT
structure was 240 microvolt k-1, bulk carrier concentration was 1.4E19 cm-3,
and two-dimensional sheet carrier concentration was 1.8E12 cm-2. When the EF
locates above the parabolic shaped conduction band bottom, rather high mobility
was observed. On the contrary, very low carrier mobility was observed when the
EF lays below the threshold, most likely due to that the tail states suppress
the carrier mobility. The present results are useful for further development of
BaSnO3 based oxide electronics.Comment: 16 pages including 4 figure
Experimental characterization of the electronic structure of anatase TiO2: Thermopower modulation
Thermopower (S) for anatase TiO2 epitaxial films (n3D: 1E17-1E21 /cm3) and
the gate voltage (Vg) dependence of S for thin film transistors (TFTs) based on
TiO2 films were investigated to clarify the electronic density of states (DOS)
around the conduction band bottom. The slope of the |S|-log n3D plots was -20
{\mu}V/K, which is an order magnitude smaller than that of semiconductors (-198
{\mu}V/K), and the |S| values for the TFTs increased with Vg in the low Vg
region, suggesting that the extra tail states are hybridized with the original
conduction band bottom.Comment: 11 pages, 4 figure
Sensory Properties in Fusion of Visual/Haptic Stimuli Using Mixed Reality
When we recognize objects, multiple sensory informa-tion (e.g., visual, auditory, and haptic) is used with fusion. For example, both eyes and hands provide rele-vant information about an object’s shape. We investi-gate how sensory stimuli interact with each other. For that purpose, we developed a system that gives hap-tic/visual sensory fusion using a mixed reality tech-nique. Our experiments show that the haptic stimulus seems to be affected by visual stimulus when a dis-crepancy exists between vision and haptic stimuli
High electrical conducting deep-ultraviolet-transparent oxide semiconductor La-doped SrSnO3 exceeding ~3000 S cm-1
La-doped SrSnO3 (LSSO) is known as one of deep-ultraviolet (DUV)-transparent
conducting oxides with an energy bandgap of ~4.6 eV. Since LSSO can be grown
heteroepitaxially on more wide bandgap substrates such as MgO (Eg ~7.8 eV),
LSSO is considered to be a good candidate as a DUV-transparent electrode.
However, the electrical conductivity of LSSO films are below 1000 S cm^-1, most
likely due to the low solubility of La ion in the LSSO lattice. Here we report
that high electrically conducting (>3000 S cm^-1) LSSO thin films with an
energy bandgap of ~4.6 eV can be fabricated by pulsed laser deposition on MgO
substrate followed by a simple annealing in vacuum. From the X-ray diffraction
and the scanning transmission electron microscopy analyses, we found that
lateral grain growth occurred during the annealing, which improved the
activation rate of La ion, leading to a significant improvement of carrier
concentration (3.26 x 10^20 cm^-3) and Hall mobility (55.8 cm^2 V^-1 s^-1). The
present DUV-transparent oxide semiconductor would be useful as a transparent
electrode for developing optoelectronic devices, which transmit and/or emit
DUV-light.Comment: 19 pages, 7 figure
Electric-Field Modulation of Thermopower for the KTaO3 Field Effect Transistors
We show herein fabrication and field-modulated thermopower for KTaO3
single-crystal based field-effect transistors (FETs). The KTaO3 FET exhibits
field effect mobility of ~8 cm2/Vs, which is ~4 times larger than that of
SrTiO3 FETs. The thermopower of the KTaO3 FET decreased from 600 to 220
microV/K by the application of gate electric field up to 1.5 MV/cm, ~400
microV/K below that of an SrTiO3 FET, clearly reflecting the smaller carrier
effective mass of KTaO3.Comment: 13 pages, 4 figure
Large-scale Filamentary Structure around the Protocluster at Redshift z=3.1
We report the discovery of a large-scale coherent filamentary structure of
Lyman alpha emitters in a redshift space at z=3.1. We carried out spectroscopic
observations to map the three dimensional structure of the belt-like feature of
the Lyman alpha emitters discovered by our previous narrow-band imaging
observations centered on the protocluster at z=3.1. The feature was found to
consist of at least three physical filaments connecting with each other. The
result is in qualitative agreement with the prediction of the 'biased'
galaxy-formation theories that galaxies preferentially formed in large-scale
filamentary or sheet-like mass overdensities in the early Universe. We also
found that the two known giant Lyman alpha emission-line nebulae showing high
star-formation activities are located near the intersection of these filaments,
which presumably evolves into a massive cluster of galaxies in the local
Universe. This may suggest that massive galaxy formation occurs at the
characteristic place in the surrounding large-scale structure at high redshift.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter
Thermoelectric phase diagram of the SrTiO3-SrNbO3 solid solution system
Thermoelectric energy conversion - the exploitation of the Seebeck effect to
convert waste heat into electricity - has attracted an increasing amount of
research attention for energy harvesting technology. Niobium-doped strontium
titanate (SrTi1-xNbxO3) is one of the most promising thermoelectric material
candidates, particularly as it poses a much lesser environmental risk in
comparison to materials based on heavy metal elements. Two-dimensional electron
confinement, e.g. through the formation of superlattices or two-dimensional
electron gases, is recognized as an effective strategy to improve the
thermoelectric performance of SrTi1-xNbxO3. Although electron confinement is
closely related to the electronic structure, the fundamental electronic phase
behavior of the SrTi1-xNbxO3 solid solution system has yet to be
comprehensively investigated. Here, we present a thermoelectric phase diagram
for the SrTi1-xNbxO3 (0.05 =< x =< 1) solid solution system, which we derived
from the characterization of epitaxial films. We observed two thermoelectric
phase boundaries in the system, which originate from the step-like decrease in
carrier effective mass at x ~ 0.3, and from a local minimum in carrier
relaxation time at x ~ 0.5. The origins of these phase boundaries are
considered to be related to isovalent/heterovalent B-site substitution:
parabolic Ti 3d orbitals dominate electron conduction for compositions with x <
0.3, whereas the Nb 4d orbital dominates when x > 0.3. At x ~ 0.5, a tetragonal
distortion of the lattice, in which the B-site is composed of Ti4+ and Nb4+
ions, leads to the formation of tail-like impurity bands, which maximizes the
electron scattering. These results provide a foundation for further research
into improving the thermoelectric performance of SrTi1-xNbxO3.Comment: 20 pages, 6 figure
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