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

TL;DR

This paper uses first-principles calculations to analyze the physical mechanisms behind the high room-temperature electron mobility in BaSnO$_3$, highlighting the roles of phonon and impurity scattering and providing insights for improving mobility.

Contribution

It provides a detailed first-principles analysis of electron transport in BaSnO$_3$, identifying key factors affecting mobility and suggesting doping strategies to mitigate impurity scattering.

Findings

High RT mobility due to small effective mass and reduced phonon scattering.

Ionized impurity scattering significantly reduces mobility at high doping levels.

Calculated Hall mobility aligns with experimental data, elucidating dominant limiting mechanisms.

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.