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