First-principles analysis of electron transport in BaSnO$_3$

Abstract

BaSnO$_3$ (BSO) is a promising transparent conducting oxide (TCO) with reported room-temperature (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 SrTiO$_3$. Using first-principles 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 ${\bf k}$ 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 $5\times10^{18}$ cm$^{-3}$, and becomes comparable to LO-phonon scattering for $1\times10^{20}$ cm$^{-3}$ doping, reducing the drift mobility from its intrinsic LO-phonon-limited value of $\sim$594 cm$^{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.