Next-generation devices require new classes of materials capable of advance (multi-) functional response. In this regard, complex-oxide materials and interfaces have the potential for far-reaching impact. Of particular interest are opportunities to harness novel light-matter interactions to enable a range of applications. Controlling such interactions requires exacting production of materials and in-depth understanding of the mechanism(s) underlying the phenomena. For example, semiconductor heterostructures drive optoelectronics for solid-state lighting, communications, computing, and sensing and the subsequent introduction of nitride- and simple oxide-based materials has helped pushed such technologies into the ultraviolet emission range. New functionalities involving ultraviolet-emitting devices may enable faster encoding and manipulation of information, new modes of chemical detection and sensing, and more efficient solid-state lighting. This project explores opportunities for on-demand complex oxide-electronics through local material reconfiguration. It builds upon discoveries of conductivity at the interface of two insulators, and demonstration of reversible, local manipulation of conductance to produce tunable ultraviolet-light emission from such materials. The project actively promotes the training of next-generation scientists and engineers in technologically important and relevant fields critical for the sustained economic vitality of the United States, focuses efforts on the mentoring and training of students from historically underrepresented groups, and provides research co-op and international research experiences for student trainees.
In this project, a new optoelectronic materials paradigm is defined by the coupling of spatially- and chemically-selective chemisorption with sub-surface quantum well(s) formed at the interface(s) of two band insulators. Symmetry-breaking and electrostatic potential mismatch between constituent semiconductors at an interface results in novel phenomena inaccessible in the bulk. This emergent phenomena can, in some systems, be tuned extensively since a surface, and to some extent, an interface, is free to reconstruct structurally and electronically. Bringing a surface or sub-surface into equilibrium with a controlled environment enables local, reversible control of the electronic phase or functional state. The effects of adsorbate type and locality, of a symmetry-lowering field on the strength, energy, and spatial response of ultraviolet luminescence from one or more distinct sub-surface, two-dimensional electron liquid(s) exhibiting electron correlations are studied. In particular, the activities focus on understanding and ultimately controlling several distinguishing features: 1) how the steady-state ultraviolet light emission intensity changes in response to different adsorbates; 2) how the physical properties of the model system, as probed by changes in spectral emission, respond to externally applied fields; 3) how the ultraviolet luminescence, including locality and stability, can be controlled with external stimuli; and 4) what the introduction of multiple, closely-spaced quantum wells and/or other oxide heterojunction materials does to the response. These investigations advance understanding of radiative recombination in new model optoelectronic ultraviolet light-emitting systems defined not by bulk, interfacial or surface properties alone, but by coupling of sub-surface interfacial quantum well electronic structure to surface chemisorption.