16 research outputs found
Effect of Sb deficiency on the thermoelectric properties of Zn4Sb3
We have investigated the effect of Sb-deficiency on the thermoelectric figure
of merit (zT) of Zn4Sb3 prepared by solid state reaction route. At high
temperatures, the Seebeck coefficient (S) and electrical conductivity
({\sigma}) increase with increase in Sb deficiency whereas the thermal
conductivity (\k{appa}) decreases giving rise to an increase in the overall zT
value. The observations suggest that creation of vacancies could be an
effective route in improving the thermoelectric properties of Zn4Sb3 system.
This coupled to nanostructuring strategy could lead to the ultimate maximum
value of zT in this system for high temperature thermoelectric applications
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
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
Large thickness dependence of the carrier mobility in a transparent oxide semiconductor, La-doped BaSnO3
We report herein that the carrier mobility of the 2%-La-doped BaSnO3 (LBSO)
films on (001) SrTiO3 and (001) MgO substrates strongly depends on the
thickness whereas it is unrelated to the lattice mismatch (+5.4% for SrTiO3,
-2.3% for MgO). Although we observed large differences in the lattice
parameters, the lateral grain size (~85 nm for SrTiO3, ~20 nm for MgO), the
surface morphology and the density of misfit dislocations, the mobility
increased almost simultaneously with the thickness in both cases and saturated
at ~100 cm2 V-1 s-1, together with the approaching to the nominal carrier
concentration (=[2% La3+]), clearly indicating that the behavior of mobility
depends on the film thickness. The present results would be beneficial to
understand the behavior of mobility and fruitful to further enhance the
mobility of LBSO films.Comment: 15 pages, including 4 figure
Buffer layer-less fabrication of high-mobility transparent oxide semiconductor, La-doped BaSnO3
Transparent oxide semiconductors (TOSs) showing both high visible
transparency and high electron mobility have attracted great attention towards
the realization of advanced optoelectronic devices. La-doped BaSnO3 (LBSO) is
one of the most promising TOSs because its single crystal exhibits a high
electron mobility. However, in the LBSO films, it is very hard to obtain high
mobility due to the threading dislocations, which are originated from the
lattice mismatch between the film and the substrate. Therefore, many
researchers have tried to improve the mobility by inserting a buffer layer.
While the buffer layers increased the electron mobilities, this approach leaves
much to be desired since it involves a two-step film fabrication process and
the enhanced mobility values are still significantly lower than single crystal
values. We show herein that the electron mobility of LBSO films can be improved
without inserting any buffer layers if the films are grown under highly
oxidative ozone (O3) atmospheres. The O3 environments relaxed the LBSO lattice
and reduced the formation of Sn2+ states, which are known to suppress the
electron mobility in LBSO. The resultant O3-LBSO films showed improved mobility
values up to 115 cm2 V-1 s-1, which is among the highest in LBSO films on
SrTiO3 substrates and comparable to LBSO films with buffer layers.Comment: 16 pages including 5 figure