11:00 〜 11:15
▼ [19a-E201-5] Origin of Mobility Suppression in La-doped BaSnO3 Films (I)
キーワード：transparent oxide semiconductor, mobility
La-doped BaSnO3 (BLSO, Pm-3m, a=4.115 Å, Eg~3.1 eV) single crystal exhibit very high mobility of 320 cm2 V−1 s−1.[1] Therefore, BLSO has attracted increasing attention as a novel transparent oxide semiconductor for advanced transparent electronic devices. Recently, many researchers were trying to realize high mobility BLSO thin films. However, the reported mobilities are still far lower than that of single crystals. The origin of mobility suppression of BLSO was considered boundary scattering at columnar domain boundaries, which are generated due to the lattice mismatch (eg. SrTiO3 +5.4 %). In order to minimize the lattice mismatch, Lee et al. used BaSnO3 single crystals as the substrates. However, the resultant mobilities were <100 cm2 V−1 s−1, [2] suggesting that the main origin is NOT lattice mismatch.
In order to clarify the main origin of the mobility suppression, we measured the electron transport properties of the BLSO (Ba0.98La0.02SnO3) epitaxial films with varied thickness (20−1000 nm), which were grown on (001) SrTiO3 (Δa=+5.4 %) or (001) MgO (Δa=−2.3 %) by PLD. Figure summarizes (a) the carrier concentration (n), (b) thermopower and (c) Hall mobility (μHall) of the resultant films as a function of the BLSO thickness at room temperature. Regarding the overall tendencies, no clear difference is observed on SrTiO3 and MgO substrates. The n increases with thickness and approaching to the nominal n (=[2.87×1020 cm−3]). The S changes simultaneously with n. The μHall also increases with thickness and reaches the maximum value of ~100 cm2 V−1 s−1.
These results clearly indicate that the lattice mismatch is not the main origin of mobility suppression but doped La3+ ions were not activated at around the film/substrate interfaces. Thus, we should clarify the origin of La3+ inactivation at around the films/substrate interfaces to improve the electron mobility of BLSO films.
In order to clarify the main origin of the mobility suppression, we measured the electron transport properties of the BLSO (Ba0.98La0.02SnO3) epitaxial films with varied thickness (20−1000 nm), which were grown on (001) SrTiO3 (Δa=+5.4 %) or (001) MgO (Δa=−2.3 %) by PLD. Figure summarizes (a) the carrier concentration (n), (b) thermopower and (c) Hall mobility (μHall) of the resultant films as a function of the BLSO thickness at room temperature. Regarding the overall tendencies, no clear difference is observed on SrTiO3 and MgO substrates. The n increases with thickness and approaching to the nominal n (=[2.87×1020 cm−3]). The S changes simultaneously with n. The μHall also increases with thickness and reaches the maximum value of ~100 cm2 V−1 s−1.
These results clearly indicate that the lattice mismatch is not the main origin of mobility suppression but doped La3+ ions were not activated at around the film/substrate interfaces. Thus, we should clarify the origin of La3+ inactivation at around the films/substrate interfaces to improve the electron mobility of BLSO films.