Juyeon Shin

High mobility BaSnO3 films and field effect transistors on non-perovskite MgO substrate

(Ba,La)SnO3 is a wide bandgap semiconducting perovskite oxide with high electron mobility and excellent oxygen stability. The carrier modulation of (Ba,La)SnO3 channel by field effect on perovskite SrTiO3 substrates has been demonstrated in the recent reports. Here we report that (Ba,La)SnO3 on non-perovskite MgO substrate can also exhibit a high electron mobility and excellent carrier modulation by field, an important step towards scaling up for wafer-size processing. We optimized the undoped buffer layer thickness and measured the transport properties as a function of the La doping. The maximum mobility is 97.2 cm2/Vs at 2.53×1020/cm3. The transmission electron microscope images show that the films are epitaxial with about 2×1011/cm2 threading dislocation density. The field effect device based on the (Ba,La)SnO3 channel on MgO substrates is modulated with a high mobility of 43.9 cm2/Vs and Ion/Ioff of about 3.0×107.

Conducting interface states at LaInO3/BaSnO3 polar interface controlled by Fermi level

We report on a new polar interface state between two band insulators: LaInO3 and BaSnO3, where the sheet conductance enhancement in the interface reaches more than the factor of 104 depending on the La doping concentration in BaSnO3 layer, by monitoring the conductance change before and after the polar interface formation as a function of La doping in BaSnO3. By eliminating the possibilities of oxygen vacancy involvement and cation diffusion, we show that the conductance enhancement is due to electronic reconstruction in the interface. Furthermore, we have found that the interfaces between BaSnO3 and the larger bandgap non-polar perovskites BaHfO3 and SrZrO3 did not show such a conductance enhancement. We discuss a model for the interface state where the Fermi level plays a critical role and the conductance enhancement is due to the existence of polarization in the polar perovskite, LaInO3.

High-k perovskite gate oxide BaHfO3

We have investigated epitaxial BaHfO3 as a high-k perovskite dielectric. From x-ray diffraction measurement, we confirmed the epitaxial growth of BaHfO3 on BaSnO3 and MgO. We measured optical and dielectric properties of the BaHfO3 gate insulator; the optical bandgap, the dielectric constant, and the breakdown field. Furthermore, we fabricated a perovskite heterostructure field effect transistor using epitaxial BaHfO3 as a gate insulator and La-doped BaSnO3 as a channel layer on SrTiO3 substrate. To reduce the threading dislocations and enhance the electrical properties of the channel, an undoped BaSnO3 buffer layer was grown on SrTiO3 substrates before the channel layer deposition. The device exhibited a field effect mobility value of 52.7 cm2 V−1 s−1, a Ion/Ioff ratio higher than 107, and a subthreshold swing value of 0.80 V dec−1. We compare the device performances with those of other field effect transistors based on BaSnO3 channels and different gate oxides.

LaInO3/BaSnO3 polar interface on MgO substrates

We report on a new property of the LaInO3 (LIO)/(Ba,La)SnO3 (BLSO) polar interface using MgO substrates. The growth of well-formed LIO/BLSO interface structures on non-perovskite MgO substrates was confirmed by reciprocal space mapping image and transmission electron microscopy. Subsequently, we measured electrical properties as a function of the La doping rate of the BLSO layer and found that the LIO/BLSO polar interface shows conductance enhancement after the deposition of the polar LaInO3 layer on the BLSO layer, in agreement with our earlier results on SrTiO3 (STO) substrates. However, different electrical properties of the interfaces were found on MgO from those on STO substrates; we observed conductance enhancement even at the interface with undoped BaSnO3 (BSO) on the MgO substrates. We attribute such different behavior to the difference in the Fermi levels of BSO on MgO and STO substrates, either due to the larger donor density or the smaller acceptor density in BSO on MgO. Using such a nominally undoped interface, we fabricated the field effect transistors and presented their performances with Ion/Ioff ∼ 109.