Chanjong Ju

High Mobility in a Stable Transparent Perovskite Oxide

We discovered that La-doped BaSnO3 with the perovskite structure has an unprecedentedly high mobility at room temperature while retaining its optical transparency. In single crystals, the mobility reached 320 cm2 V-1 s-1 at a doping level of 8×1019 cm-3, constituting the highest value among wide-band-gap semiconductors. In epitaxial films, the maximum mobility was 70 cm2 V-1 s-1 at a doping level of 4.4×1020 cm-3. We also show that resistance of (Ba,La)SnO3 changes little even after a thermal cycle to 530 °C in air, pointing to an unusual stability of oxygen atoms and great potential for realizing transparent high-frequency, high-power functional devices.

All-perovskite transparent high mobility field effect using epitaxial BaSnO3 and LaInO3

We demonstrate an all-perovskite transparent heterojunction field effect transistor made of two lattice-matched perovskite oxides: BaSnO3 and LaInO3. We have developed epitaxial LaInO3 as the gate oxide on top of BaSnO3, which were recently reported to possess high thermal stability and electron mobility when doped with La. We measured the dielectric properties of the epitaxial LaInO3 films, such as the band gap, dielectric constant, and the dielectric breakdown field. Using the LaInO3 as a gate dielectric and the La-doped BaSnO3 as a channel layer, we fabricated field effect device structure. The field effect mobility of such device was higher than 90 cm2 V−1 s−1, the on/off ratio was larger than 107, and the subthreshold swing was 0.65 V dec−1. We discuss the possible origins for such device performance and the future directions for further improvement.

High-mobility BaSnO3 thin-film transistor with HfO2 gate insulator

Thin-film transistors have been fabricated using La-doped BaSnO3 as n-type channels and (In,Sn)2O3 as source, drain, and gate electrodes. HfO2 was grown as gate insulators by atomic layer deposition. The field-effect mobility, Ion/Ioff ratio, and subthreshold swing of the device are 24.9 cm2 V−1 s−1, 6.0 × 106, and 0.42 V dec−1, respectively. The interface trap density, evaluated to be higher than 1013 cm−2 eV−1, was found to be slightly lower than that of the thin-film transistor with an Al2O3 gate insulator. We attribute the much smaller subthreshold swing values to the higher dielectric constant of HfO2.

High electron mobility in epitaxial SnO2−x in semiconducting regime

We investigated the electronic transport properties of epitaxial SnO2−x thin films on r-plane sapphire substrates. The films were grown by pulsed laser deposition technique and its epitaxial growth direction was [101] and the in-plane alignment was of SnO2−x [010]//Al2O3[1210]. When the SnO2−x films were grown in the oxygen pressure of 30 mTorr, we have found the electron mobility of the 30 nm thick SnO2−x thin films strongly dependent on the thicknesses of the fully oxidized insulating SnO2 buffer layer. When the buffer layer thickness increased from 100 nm to 700 nm, the electron mobility of values increased from 23 cm2 V−1 s−1 to 106 cm2 V−1 s−1 and the carrier density increased from 9 × 1017 cm−3 to 3 × 1018 cm−3, which we attribute to reduction of large density of dislocations as the buffer layer thickness increases. In addition, we studied the doping dependence of the electron mobility of SnO2−x thin films grown on top of 500 nm thick insulating SnO2 buffer layers. The oxygen vacancy doping level w...