A consistent picture of excitations in cubic BaSnO3 revealed by combining theory and experiment

Wahib Aggoune,Zbigniew Galazka,Claudia Draxl,Klaus Irmscher,Martina Zupancic,Christoph Koch,Alberto Eljarrat,Martin Albrecht,Dmitrii Nabok

doi:10.1038/s43246-022-00234-6

Abstract

Among the transparent conducting oxides, the perovskite barium stannate is most promising for various electronic applications due to its outstanding carrier mobility achieved at room temperature. However, most of its important characteristics, such as band gaps, effective masses, and absorption edge, remain controversial. Here, we provide a fully consistent picture by combining state-of-the-art ab initio methodology with forefront electron energy-loss spectroscopy and optical absorption measurements. Valence electron energy-loss spectra, featuring signals originating from band gap transitions, are acquired on defect-free sample regions of a BaSnO3 single crystal. These high-energy-resolution measurements are able to capture also very weak excitations below the optical gap, attributed to indirect transitions. By temperature-dependent optical absorption measurements, we assess band-gap renormalization effects induced by electron-phonon coupling. Overall, we find for the effective electronic mass, the direct and the indirect gap, the optical gap, as well as the absorption onsets and spectra, excellent agreement between both experimental techniques and the theoretical many-body results, supporting also the picture of a phonon-mediated mechanism where indirect transitions are activated by phonon-induced symmetry lowering. This work demonstrates a fruitful connection between different high-level theoretical and experimental methods for exploring the characteristics of advanced materials.

Highlights

Among the transparent conducting oxides, the perovskite barium stannate is most promising for various electronic applications due to its outstanding carrier mobility achieved at room temperature
BaSnO3, when doped with lanthanum, has turned out as the most promising candidate for the generation of electronic devices. This is mainly due to the combination of extraordinary roomtemperature mobility, reaching 320 cm[2] V−1 s−1—which is the highest ever measured in Transparent conducting oxides (TCO)—and a significant degree of transparency in the visible range[1]
Considering the formal ionic charges of Ba (+2), Sn (+4), and O (−2), BaSnO3 is formed by alternating neutral BaO and SnO2 layers along the [100], [010], and [001] directions, making it a nonpolar material

Summary

Introduction

Among the transparent conducting oxides, the perovskite barium stannate is most promising for various electronic applications due to its outstanding carrier mobility achieved at room temperature. Valence electron energy-loss spectra, featuring signals originating from band gap transitions, are acquired on defect-free sample regions of a BaSnO3 single crystal These high-energy-resolution measurements are able to capture very weak excitations below the optical gap, attributed to indirect transitions. BaSnO3, when doped with lanthanum, has turned out as the most promising candidate for the generation of electronic devices This is mainly due to the combination of extraordinary roomtemperature mobility, reaching 320 cm[2] V−1 s−1—which is the highest ever measured in TCOs—and a significant degree of transparency in the visible range[1]. As an alternative to La-doping, an exciting perspective has been opened by polar-discontinuity doping, i.e., by forming interfaces or heterostructures of the nonpolar BaSnO3 with a polar oxide perovskite In this case, a high-mobility two-dimensional electron gas can be formed in BaSnO3 without doping[4,8–14]

Methods

Results

Conclusion