Abstract
The scattering of charge carriers by line defects, i.e., threading dislocations (TDs), severely limits electron mobility in epitaxial semiconductor films grown on dissimilar substrates. The density of TDs needs to be decreased to further enhance electron mobility in lattice-mismatched epitaxial films and heterostructures for application in high-performance electronic devices. Here, we report a strategy for the post-treatment of epitaxial La-doped BaSnO3 (LBSO) films by delicately controlling the oxygen partial pressure p(O2), which achieved a significant increase in the room temperature (RT) electron mobility (μe) to μe = 122 cm2 V−1 s−1 at a carrier concentration of 1.1 × 1020 cm−3. This mobility enhancement is mostly attributed to an oxygen vacancy-assisted recovery process that reduces the density of TDs by accelerating the movement of dislocations in ionic crystals under a p(O2)-controlled treatment despite an increase in the density of charged point defects. Our finding suggests that accurate control of the interactions between point defects and line defects can reduce dominant carrier scattering by charged dislocations in epitaxial oxide semiconductors that have dissimilar substrates. This method provides alternative approaches to achieving perovskite oxide heterostructures that have high RT μe values.
Highlights
Heteroepitaxial growth is the epitaxial growth of semiconductor films on dissimilar substrates (e.g., GaN on Al2O3); it has been widely used to obtain single-crystal films for electronic and photonic applications mostly because of the limited availability of single-crystal semiconductor substrates with identical lattice parameters for homoepitaxial growth[1,2]
~70 cm[2] V−1 s−1 by pulsed laser deposition (PLD)[11] and ~124 cm[2] V−1 s−1 by molecular beam epitaxy (MBE)13) than single crystals[11]. This low μe has been attributed to the abundance of TDs9 that inevitably form during epitaxial growth due to large lattice mismatch with the substrate, e.g., SrTiO3 or MgO
The as-grown 1% La-doped BaSnO3 (LBSO) epitaxial films exhibited the parameters n ~5.3 × 1019 cm−3 and room temperature (RT) μe ~15 cm[2] V−1 s−1 when grown on STO and n ~4.1 × 1019 cm−3 and RT μe ~16 cm[2] V−1 s−1 when grown on MgO (Fig. 1, Fig. S1); these values are comparable to those of other as-grown 1% LBSO epitaxial films produced by PLD (n ~6 × 1019 cm−3, μe ~20 cm[2] V−1 s−1)[11,21]
Summary
Heteroepitaxial growth is the epitaxial growth of semiconductor films on dissimilar substrates (e.g., GaN on Al2O3); it has been widely used to obtain single-crystal films for electronic and photonic applications mostly because of the limited availability of single-crystal semiconductor substrates with identical lattice parameters for homoepitaxial growth[1,2]. Heteroepitaxial layers contain high densities of structural defects; because of the lattice mismatch between films and substrates, most of the defects are threading dislocations (TDs), which cross the epitaxial layers perpendicularly[2,3]. ~70 cm[2] V−1 s−1 by pulsed laser deposition (PLD)[11] and ~124 cm[2] V−1 s−1 by molecular beam epitaxy (MBE)13) than single crystals[11]. This low μe has been attributed to the abundance of TDs9 that inevitably form during epitaxial growth due to large lattice mismatch with the substrate, e.g., SrTiO3 or MgO. Considerable effort has been devoted to decreasing the density of TDs by using substrates with a lattice constant that is similar to or even the same as that of BSO13–16 or by inserting buffer layers between BSO epilayers and typical substrates[12,17,18,19] to release the lattice mismatch strain
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