First-principles analysis of electron transport in BaSnO3

Abstract

BaSnO3 (BSO) is a promising transparent conducting oxide (TCO) with reported roomtemperature (RT) Hall mobility exceeding 320 cm 2 V −1 s −1 . Among perovskite oxides, it has the highest RT mobility, about 30 times higher than that of the prototypical SrTiO3. Using firstprinciples calculations based on hybrid density functional theory, we elucidate the physical mechanisms that govern the mobility by studying the details of LO-phonon and ionized impurity scattering. A careful numerical analysis to obtain converged results within the relaxation-time approximation of Boltzmann transport theory is presented. The k dependence of the relaxation time is fully taken into account. We find that the high RT mobility in BSO originates not only from a small effective mass, but also from a significant reduction in the phonon scattering rate compared to other perovskite oxides; the origins of this reduction are identified. Ionized impurity scattering influences the total mobility even at RT for dopant densities larger than 5 × 10 18 cm −3 , and becomes comparable to LO-phonon scattering for 1 × 10 20 cm −3 doping, reducing the drift mobility from its intrinsic LO-phonon-limited value of ∼594 cm 2 V −1 s −1 to less than 310 cm 2 V −1 s −1 . We suggest pathways to avoid impurity scattering via modulation doping or polar discontinuity doping. We also explicitly calculate the Hall factor and Hall mobility, allowing a direct comparison to experimental reports for bulk and thin films and providing insights into the nature of the dominant mechanisms that limit mobility in state-of-the art samples.

Electron effective mass and mobility limits in degenerate perovskite stannateBaSnO3

“…For carrier concentrations above 1 × 10 20 cm −3 , the room temperature mobility in BaSnO 3 is governed by electron-phonon interactions and electron scattering at ionized La impurities [30]. The mobility governed by longitudinal optical (LO) phonon scattering is calculated according to [31,32] …”

“…Solid lines present theoretical calculation of the mobility using the three analytical scattering models according to Eqs. (9), (11), (12) and Ga 2 O 3 (∼115 cm 2 /Vs [42]), allowing to achieve an extraordinary high ∼300 cm 2 /Vs mobility even at room temperature [24,30].…”

“…Solid lines present theoretical calculation of the mobility using the three analytical scattering models according to Eqs. (9), (11), (12) and Ga 2 O 3 (∼115 cm 2 /Vs [42]), allowing to achieve an extraordinary high ∼300 cm 2 /Vs mobility even at room temperature [24,30].Further progress in the development of BaSnO 3 epitaxial films for application in transparent oxide electronics may be realized not only by considering the lattice mismatch with the substrate, but also by optimising epitaxial growth techniques to reduce dislocation densities and domain boundaries which are inherent to the perovskite structure.Selective-area growth and epitaxial lateral overgrowth techniques as successfully applied 10 in III-nitride semiconductor technology [43] may present effective methods for achieving higher mobilities by reducing the dislocation density of the present BaSnO 3 epitaxial films.In conclusion, degenerate perovskite BaSnO 3 exhibits an extraordinary high room temperature mobility attributed to an electron effective mass as small as 0.19 m 0 . An in-depth investigation of the infrared free carrier absorption and the Burstein-Moss shift yields a significant dependence of electron effective mass on doping level, concurrent with a pronounced non-parabolicity of the conduction band.…”

Intrinsic Carrier Mobility of Cesium Lead Halide Perovskites

“…All the parameters for calculating the transport properties are obtained from first-principles calculations and, therefore, the present approach is fully ab initio. We focus on electron-phonon scattering by polar longitudinal-optical (LO) phonon modes that are the dominant scattering source in polar materials due to polarity and long-range character [17,18]. The coupling of an electron to the polar LO modes is described by the generalized Fröhlich model [17].…”

“…We focus on electron-phonon scattering by polar longitudinal-optical (LO) phonon modes that are the dominant scattering source in polar materials due to polarity and long-range character [17,18]. The coupling of an electron to the polar LO modes is described by the generalized Fröhlich model [17]. The room-temperature carrier mobility is then evaluated by Boltzmann transport theory within the relaxationtime approximation, providing the intrinsic limit of the mobility.…”