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Complex oxides such as tin-doped indium oxide (ITO) are widely utilized as transparent conductors in a variety of functional devices. Typically, they are fabricated by sputtering, which often requires additional annealing to achieve high transparency and conductivity. Using pulsed laser deposition (PLD), both high transparency and high conductivity have been achieved without annealing, using instead selected gas species and pressures. However, the relative roles of Stranski-Krastanov-like and vapor-liquid-solid (VLS) growth modes during morphological transitions remain controversial. Here, we report on PLD of ITO in an inert-gas environment, identifying the role of plasma-plume expansion in the selection of VLS vs vapor-solid (VS) growth. For the lowest N2 pressure, indium-tin droplet formation, followed by self-catalyzed VLS growth, is observed. With increasing N2 pressure, a transition from VLS to VS growth is apparent. It is hypothesized that oxygen scattering at the lowest N2 pressure induces a metal-rich plume, which leads to metal droplet formation, followed by VLS growth. As the N2 pressure is increased, the plasma-plume and its metal-rich core are compressed, resulting in a transition to VS growth. This tunable compression of the plasma-plume offers a route to the morphological design of a wide range of functional complex oxide devices with tunable optical and electronic performance. [ABSTRACT FROM AUTHOR]

Author(s): J. T. Heron (corresponding author) [1]; J. L. Bosse [2]; Q. He [3]; Y. Gao [4, 5]; M. Trassin [6]; L. Ye [2]; J. D. Clarkson [7]; C. Wang [...]

Ultra-wide-band-gap (UWBG) semiconductors have tremendous potential to advance electronic devices as device performance improves superlinearly with the increasing gap. Ambipolar doping, however, has been a major challenge for UWBG materials as dopant ionization energy and charge compensation generally increase with the increasing bandgap and significantly limit the semiconductor devices that can currently be realized. Using hybrid density functional theory, we demonstrate rutile germanium oxide (r-GeO2) to be an alternative UWBG (4.68 eV) material that can be ambipolarly doped. We identify SbGe, AsGe, and FO as possible donors with low ionization energies and propose growth conditions to avoid charge compensation by deep acceptors such as VGe and NO. On the other hand, acceptors such as AlGe have relatively large ionization energies (0.45 eV) due to the formation of localized hole polarons and are likely to be passivated by VO, Gei, and self-interstitials. Yet, we find that the co-incorporation of AlGe with interstitial H can increase the solubility limit of Al and enable hole conduction in the impurity band. Our results show that r-GeO2 is a promising UWBG semiconductor that can overcome current doping challenges and enable the next generation of power electronics devices. [ABSTRACT FROM AUTHOR]

Conventional CMOS based logic and magnetic based data storage devices require the shuttling of electrons for data processing and storage. As these devices are scaled to increasingly smaller dimensions in the pursuit of speed and storage density, significant energy dissipation in the form of heat has become a center stage issue for the microelectronics industry. By taking advantage of the strong correlations between ferroic orders in multiferroics, specifically the coupling between ferroelectric and magnetic orders (magnetoelectricity), new device functionalities with ultra-low energy consumption can be envisioned. In this article, we review the advances and highlight challenges toward this goal with a particular focus on the room temperature magnetoelectric multiferroic, BiFeO3, exchange coupled to a ferromagnet. We summarize our understanding of the nature of exchange coupling and the mechanisms of the voltage control of ferromagnetism observed in these heterostructures. [ABSTRACT FROM AUTHOR]

The manipulation of antiferromagnetic order in magnetoelectric Cr2O3 using electric field has been of great interest due to its potential in low-power electronics. The substantial leakage and low dielectric breakdown observed in twinned Cr2O3 thin films, however, hinders its development in energy efficient spintronics. To compensate, large film thicknesses (250 nm or greater) have been employed at the expense of device scalability. Recently, epitaxial V2O3 thin film electrodes have been used to eliminate twin boundaries and significantly reduce the leakage of 300 nm thick single crystal films. Here we report the electrical endurance and magnetic properties of thin (less than 100 nm) single crystal Cr2O3 films on epitaxial V2O3 buffered Al2O3 (0001) single crystal substrates. The growth of Cr2O3 on isostructural V2O3 thin film electrodes helps eliminate the existence of twin domains in Cr2O3 films, therefore significantly reducing leakage current and increasing dielectric breakdown. 60 nm thick Cr2O3 films show bulk-like resistivity (~ 1012 Ω cm) with a breakdown voltage in the range of 150–300 MV/m. Exchange bias measurements of 30 nm thick Cr2O3 display a blocking temperature of ~ 285 K while room temperature optical second harmonic generation measurements possess the symmetry consistent with bulk magnetic order. [ABSTRACT FROM AUTHOR]

High-quality epitaxial thin films of Jeff = 1/2 Mott insulator Sr2IrO4 with increasing in-plane tensile strain have been grown on top of SrTiO3(001) substrates. Increasing the in-plane tensile strain up to ~0.3% was observed to drop the c/a tetragonality by 1.2%. X-ray absorption spectroscopy detected a strong reduction of the linear dichroism upon increasing in-plane tensile strain towards a reduced anisotropy in the local electronic structure. While the most relaxed thin film shows a consistent dependence with previously reported single crystal bulk measurements, electrical transport reveals a charge gap reduction from 200 meV down to 50 meV for the thinnest and most epitaxy-distorted film. We argue that the reduced tetragonality plays a major role in the change of the electronic structure, which is reflected in the change of the transport properties. Our work opens the possibility for exploiting epitaxial strain as a tool for both structural and functional manipulation of spin-orbit Mott systems. [ABSTRACT FROM AUTHOR]

We report direct experimental evidence for a room-temperature, ~130 µC/cm² ferroelectric polarization from the tetragonal-like BiFeO3 phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octabedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase. [ABSTRACT FROM AUTHOR]