Daniela F. Bogorin

Creation of a two-dimensional electron gas at an oxide interface on silicon

In recent years, reversible control over metal-insulator transition has been shown, at the nanoscale, in a two-dimensional electron gas (2DEG) formed at the interface between two complex oxides. These materials have thus been suggested as possible platforms for developing ultrahigh-density oxide nanoelectronics. A prerequisite for the development of these new technologies is the integration with existing semiconductor electronics platforms. Here, we demonstrate room-temperature conductivity switching of 2DEG nanowires formed at atomically sharp LaAlO(3)/SrTiO(3) (LAO/STO) heterointerfaces grown directly on (001) Silicon (Si) substrates. The room-temperature electrical transport properties of LAO/STO heterointerfaces on Si are comparable with those formed from a SrTiO(3) bulk single crystal. The ability to form reversible conducting nanostructures directly on Si wafers opens new opportunities to incorporate ultrahigh-density oxide nanoelectronic memory and logic elements into well-established Si-based platforms.

“Water-cycle” mechanism for writing and erasing nanostructures at the LaAlO3/SrTiO3 interface

Nanoscale control of the metal-insulator transition in LaAlO3/SrTiO3 heterostructures can be achieved using local voltages applied by a conductive atomic force microscope (c-AFM) probe. One proposed mechanism for such process involves adsorbed H2O which dissociates into OH− and H+ which are then selectively removed by a biased AFM probe. To test this mechanism, writing and erasing experiments are performed in a vacuum AFM using various gas mixtures. Writing ability is suppressed in those environments where H2O is not present. The self-erasure process in air can be strongly suppressed by creating a modest vacuum or replacing the humid air with dry inert gas. These experiments provide strong constraints for theories of both the writing process as well as the origin of interfacial conductance.

Rewritable nanoscale oxide photodetector

Researchers report rewritable nanoscale photodetectors that exploit 2–3 nm nanowire junctions. Large electromagnetic fields in the gap region aid the detector response, which is electric-field-tunable and spans the visible to near-infrared regime.

Nanoscale rectification at the LaAlO3/SrTiO3 interface

Nanoscale control over electron transport at scales that are comparable to the Fermi wavelength or mean-free path can lead to new families of electronic devices. Here we report electrical rectification in nanowires formed by nanoscale control of the metal-insulator transition at the interface between LaAlO3 and SrTiO3. Controlled in-plane asymmetry in the confinement potential produces electrical rectification in the nanowire, analogous to what occurs naturally for Schottky diodes or by design in structures with engineered structural inversion asymmetry. Nanostructures produced in this manner may be useful for electro-optic applications or in spintronic devices.

Oxide-based platform for reconfigurable superconducting nanoelectronics

We report superconductivity in quasi-1D nanostructures created at the LaAlO3/SrTiO3 interface. Nanostructures having line widths w~10 nm are formed from the parent two-dimensional electron liquid using conductive atomic force microscope lithography. Nanowire cross-sections are small compared to the superconducting coherence length in LaAlO3/SrTiO3 (w<<xi~100 nm), placing them in the quasi-1D regime. Broad superconducting transitions with temperature and finite resistances in the superconducting state well below Tc~200 mK are observed. V-I curves show switching between the superconducting and normal states that are characteristic of superconducting nanowires. The four-terminal resistance in the superconducting state shows an unusual dependence on the current path, varying by as much as an order of magnitude.

Thermal activation and quantum field emission in a sketch-based oxide nanotransistor

We report direct measurements of the potential barriers and electronic coupling between nanowire segments within a sketch-based oxide nanotransistor (SketchFET) device. Near room temperature, switching is governed by thermal activation across a potential barrier controlled by the nanowire gate. Below T = 150 K, current flow is dominated by quantum field emission. Sharp maxima in the quantum field emission, observed at T(C1) = 65 K and T(C2) = 25 K, arise from dielectric anomalies occurring at structural phase transitions in the SrTiO(3) layer. This direct measurement of the source-drain and gate-drain energy barriers is crucial for the development of room-temperature logic and memory elements and low-temperature quantum devices.