Nonequilibrium dynamics of perovskite wide-bandgap oxides under high-density carrier injection

Wide bandgap oxides (WBGOs) have widely emerged in modern photonics such as transparent conducting oxides in photovoltaics or gate oxides in power electronics [1~4]. Perovskite WBGOs provide the additional advantage of seamless integration with extended functionalities such as ferroelectricity and superconductivity in other perovskites, enabling future compact multifunctional devices [5,6]. Barium stannate (BaSnO₃, BSO) recently rose as the most studied perovskite WBGO for its wide doping range and outstanding electron mobility of 320 cm²/(Vs) among WBGOs [7]. The low electron effective mass at conduction band minimum, mainly composed of the strong antibonding Sn 5s-orbital, explained its superior mobility. However, transient electronic structural dynamics of BSO immediately after carrier injection into the conduction band is not easily accessed and thus has not been fully understood. The early fate of injected carriers is deterministic for the ultimate formation of photocurrent in photovoltaics as well as reliability in power electronics. In this study, we mimic transient carrier injection into BSO via ultrafast above-gap photoexcitation and revealed its sub-picosecond carrier dynamics with UV transient absorption (TA) spectroscopy across the bandgap. A fast hot-carrier cooling lifetime of 1ps due to electron-phonon scattering along with clear exciton bleach and excitonic enhancement resulting from photo-excited free carriers are unveiled.

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[4] I. Hussain, et al., Emergent Mater. 1, 133 (2018).

[5] W.-J. Lee, et al., Annual Review of Materials Research 47, 391 (2017).

[6] U. Kim, et al., APL Materials 3, 036101 (2015).

[7] H. J. Kim, et al., Appl. Phys. Express 5, 061102 (2012).