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Register a new userTransparent perovskite barium stannate with high electron mobility and thermal stability
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Transparent conducting oxides (TCOs) and transparent oxide semiconductors (TOSs) have become necessary materials for a variety of applications in the information and energy technologies, ranging from transparent electrodes to active electronics components. Perovskite barium stannate (BaSnO3), a new TCO or TOS system, is a potential platform for realizing optoelectronic devices and observing novel electronic quantum states due to its high electron mobility, excellent thermal stability, high transparency, structural versatility, and flexible doping controllability at room temperature. This article reviews recent progress in the doped BaSnO3 system, discussing the wide physical properties, electron-scattering mechanism, and demonstration of key semiconducting devices such as pn diodes and field-effect transistors. Moreover, we discuss the pathways to achieving two-dimensional electron gases at the interface between BaSnO3 and other perovskite oxides and describe remaining challenges for observing novel quantum phenomena at the heterointerface.
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The high room temperature mobility and the electron effective mass in BaSnO$_3$ are investigated in depth by evaluation of the free carrier absorption observed in infrared spectra for epitaxial films with free electron concentrations from $8.3 times 10^{18}$ to $7.3 times 10^{20}$~cm$^{-3}$. Both the optical band gap widening by conduction band filling and the carrier scattering mechanisms in the low and high doping regimes are consistently described employing parameters solely based on the intrinsic physical properties of BaSnO$_3$. The results explain the current mobility limits in epitaxial films and demonstrate the potential of BaSnO$_3$ to outperform established wide band gap semiconductors also in the moderate doping regime.
Contrary to the common belief that electron-electron interaction (EEI) should be negligible in s-orbital-based conductors, we demonstrated that the EEI effect could play a significant role on electronic transport leading to the misinterpretation of the Hall data. We show that the EEI effect is primarily responsible for an increase in the Hall coefficient in the La-doped SrSnO3 films below 50 K accompanied by an increase in the sheet resistance. The quantitative analysis of the magnetoresistance (MR) data yielded a large phase coherence length of electrons exceeding 450 nm at 1.8 K and revealed the electron-electron interaction being accountable for breaking of electron phase coherency in La-doped SrSnO3 films. These results while providing critical insights into the fundamental transport behavior in doped stannates also indicate the potential applications of stannates in quantum coherent electronic devices owing to their large phase coherence length.
Transition metal perovskite chalcogenides, a class of materials with rich tunability in functionalities, are gaining increased attention as candidate materials for renewable energy applications. Perovskite oxides are considered excellent n-type thermoelectric materials. Compared to oxide counterparts, we expect the chalcogenides to possess more favorable thermoelectric properties such as lower lattice thermal conductivity and smaller band gap, making them promising material candidates for high temperature thermoelectrics. Thus, it is necessary to study the thermal properties of these materials in detail, especially thermal stability, to evaluate their potential. In this work, we report the synthesis and thermal stability study of five compounds, alpha-SrZrS$_3$, beta-SrZrS$_3$, BaZrS$_3$, Ba$_2$ZrS$_4$, and Ba$_3$Zr$_2$S$_7$. These materials cover several structural types including distorted perovskite, needle-like, and Ruddlesden-Popper phases. Differential scanning calorimeter and thermo-gravimetric analysis measurements were performed up to 1200{deg}C in air. Structural and chemical characterizations such as X-ray diffraction, Raman spectroscopy, and energy dispersive analytical X-ray spectroscopy were performed on all the samples before and after the heat treatment to understand the oxidation process. Our studies show that perovskite chalcogenides possess excellent thermal stability in air at least up to 600{deg}C.
We discovered that perovskite (Ba,La)SnO3 can have excellent carrier mobility even though its band gap is large. The Hall mobility of Ba0.98La0.02SnO3 crystals with the n-type carrier concentration of sim 8-10times10 19 cm-3 is found to be sim 103 cm2 V-1s-1 at room temperature, and the precise measurement of the band gap Delta of a BaSnO3 crystal shows Delta=4.05 eV, which is significantly larger than those of other transparent conductive oxides. The high mobility with a wide band gap indicates that (Ba,La)SnO3 is a promising candidate for transparent conductor applications and also epitaxial all-perovskite multilayer devices.
Transparent conductors-nearly an oxymoron-are in pressing demand, as ultra-thin-film technologies become ubiquitous commodities. As current solutions rely on non-abundant elements, perovskites such as SrVO3 and SrNbO3 have been suggested as next generation transparent conductors. Our ab-initio calculations and analytical insights show, however, that reducing the plasma frequency below the visible spectrum by strong electronic correlations-a recently proposed strategy-unavoidably comes at a price: an enhanced scattering and thus a substantial optical absorption above the plasma edge. As a way out of this dilemma we identify several perovskite transparent conductors, relying on hole doping, somewhat larger bandwidths and separations to other bands.
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