arXiv subjects

Anup V. Sanchela

Publications and source records attributed to Anup V. Sanchela.

12 recordsLinked to original sources

arXiv2021

Direction dependent thermoelectric properties of layered compound In2Te5 single crystal

We analyze the anisotropic electrical and thermal transport measurements in single crystals of In2Te5 belonging to monoclinic space group C12 c1 with the temperature gradient applied parallel and perpendicular to the crystallographic c-axis of the crystals. The thermal conductivity along the c-axis thermal conductivity parallel was found to smaller by a factor of 2 compared to the thermal conductivity along the direction perpendicular to the c-axis over the entire temperature range. In contrast, the Seebeck coefficient along the c-axis parallel was found to be higher than its value along the direction perpendicular to the c-axis. At room temperature, the figure of merit ZT parallel is found to be 4 times larger as compared to the figure of merit ZT perpendicular.

cond-mat.mtrl-sci↗

arXiv2019

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.

cond-mat.mtrl-sci↗

arXiv2018

Oxygen vacancy driven mobility enhancement in epitaxial La-doped BaSnO3 from vacuum annealing

Wide bandgap (~3.1 eV) La-doped BaSnO3 (LBSO) has attracted increasing attention as one of the transparent oxide semiconductors since its bulk single crystal shows a high carrier mobility (~320 cm2 V-1 s-1) with a high carrier concentration (~10^20 cm-3). For this reason, many researchers have fabricated LBSO epitaxial films thus far, but the obtainable carrier mobility is substantially low compared to that of single crystals due to the formation of the lattice/structural defects. Here we report that the mobility suppression in LBSO films can be lifted by a simple vacuum annealing process. The vacuum annealing of the LBSO films on MgO substrate increased the carrier concentrations due to the oxygen vacancy formation, which leads to simultaneous lateral grain growth. As a result, the carrier mobility was greatly improved by the vacuum annealing, which does not occur after heat treatment in air. These results expand our current knowledge on the point defect formation in epitaxial LBSO films and show that vacuum annealing is a powerful tool for enhancing the mobility values of LBSO films.

cond-mat.mtrl-sci↗

arXiv2018

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.

cond-mat.mtrl-sci↗

arXiv2018

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.

cond-mat.mtrl-sci↗

arXiv2017

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.

cond-mat.mtrl-sci↗

arXiv2016

n-type SnSe$_{1-x}$ for Thermoelectric Application

We report the synthesis of n-type SnSe$_{1-x}$ using a self-sacrificial, facile, solvo-thermal synthesis route. Electrical and thermal transport measurements suggest a low thermal conductivity and a significant thermopower in the temperature range 100 - 400\,K. We also propose the possibility of developing an all SnSe thermoelectric module.

cond-mat.mtrl-sci↗

arXiv2015

Cu2ZnSnS4 Films using an Eco-friendly Direct Liquid Coating Approach for Solar Cell Applications

Cu2ZnSnS4 (CZTS) is a promising candidate as an absorber material for thin film solar cells. The reported wet chemical synthesis approaches often have a high environmental impact due to the usage of abrasive solvents such as hydrazines, hydroxylamines, etc. We report an eco-friendly solvent based approach for making CZTS thin films with desirable absorption characteristics for solar cell applications.

cond-mat.mtrl-sci↗

arXiv2015

Improvement in thermoelectric properties by tailoring at In and Te site in In2Te5

We study role of site substitutions at In and Te site in In2Te5 on the thermoelectric behavior. Single crystals with compositions In2(Te1-xSex)5 (x = 0, 0.05, 0.10) and Fe0.05In1.95(Te0.90Se0.10)5 were prepared using modified Bridgman-Stockbarger technique. Electrical and thermal transport properties of these single crystals were measured in the temperature range 6 - 395 K. A substantial decrease in thermal conductivity is observed in Fe substituted samples attributed to the enhanced phonon point-defect scattering. Marked enhancement in Seebeck coefficient S along with a concomitant suppression of electrical resistivity \r{ho} is observed in Se substituted single crystals. An overall enhancement of thermoelectric figure of merit (zT) by a factor of 310 is observed in single crystals of Fe0.05In1.95(Te0.90Se0.10)5 compared to the parent In2Te5 single crystals.

cond-mat.mtrl-sci↗

arXiv2015

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 (σ) 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.

cond-mat.mtrl-sci↗

arXiv2015

Enhancement in thermoelectric properties of FeSb2 by Sb site deficiency

We report a strategy based on introduction of point defects for improving the thermoelectric properties of FeSb2, a promising candidate for low temperature applications. Introduction of Sb deficiency to the tune of 20% leads to enhancement in the values of electrical conductivity (σ) and Seebeck coefficient (S) accompanied with a concomitant suppression in lattice thermal conductivity (\k{appa}lat) values in samples prepared using conventional solid state reaction route. These observations in polycrystalline FeSb2-x provides ample motivation for a dedicated exploration of thermoelectric behavior of the corresponding single crystalline as well as hot-pressed polycrystalline counterparts.

cond-mat.mtrl-sci↗

arXiv2012

Nanostructured Zinc Oxide as a Prospective Room Temperature Thermoelectric Material

Nanostructured Zinc oxide (ZnO) was synthesized via a ball milling for 10 hours using high energy planetary ball mill. Phase purity and homogeneity of all the samples have been investigated by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM). All the diffraction peaks can be indexed to the hexagonal phase ZnO with hexagonal symmetry (space group P63mc). Average crystallite size was observed to be 20 nm. There was a remarkable suppression in thermal conductivity (κ) compared to the bulk values by a factor of ~50 at room temperature. This suggests to the possibility of using nanostructured ZnO as a prospective room temperature thermoelectric material.

cond-mat.mtrl-sci↗