Polarization-Driven Electron-Hole Bilayers in Quantum Wells

Cornell University, Ithaca NY

Investigators

Abstract

Non-technical description: This project aims to discover new electronic and optical phenomena hidden in a material system that is currently used in solid state lighting, in communication systems, and power electronics, and is in almost all iPhones and iPads. The research focuses on electrical charge carriers of opposite signs located very close to each other in gallium nitride quantum structures. The carriers of opposite signs maintain separate identities, until they receive a command (for example through a small voltage or a current), upon which they mix strongly to either emit light, or flow as currents with very little energy dissipation. This sort of phenomena has been long desired for making low-power or ultrafast and energy-efficient electronic switches, for photonic devices, and potentially for sensor environments. Thus, findings of this project have a potential to impact the electronics and photonics industries, and environmental health and safety systems. The project trains graduate students in a fascinating emerging field at the intersection of physics, materials science, and electrical engineering. In addition to expanding existing outreach programs, new activities are considered with a special focus on the high-school students and underrepresented groups, including direct school visits and in-class demonstrations. The dissemination of research results in journal publications, presentations at conferences and inclusion in courses taught by the PI made available online ensures the outreach to the widest possible audience. Technical description: This project explores the quantum transport and optical properties of III-nitride quantum structures and their potential applications in electron-hole bilayer systems, driven by large polarization fields. Such bilayers are difficult to create in other material systems either because of the lack of polarization, doping limitations, or because of low breakdown fields. When created (for example, in two-dimensional layered materials), additional challenges occur related to their chemical doping and contact reliability. In this project, the PI takes advantage of unique recent technological progress in epitaxially regrown contacts to two-dimensional electron and hole gases in novel compressively strained GaN quantum wells on AlN substrates to explore bilayer physics in a fundamentally new platform. Parallel two-dimensional systems of electrons and holes boast rich physics at several levels of complexity - from uncoupled two-dimensional electron-gas / two-dimensional hole gas p-n diodes that could lead to new electronic and photonic devices, to weakly coupled systems, exhibiting Coulomb drag, to strongly coupled systems that have shown glimpses of excitonic or Bose-Einstein condensation. And with the tantalizing possibility of polarization-driven topological edge states, the outcomes of the project has a potential for significant scientific and technological advances for ultra-low power electronic, photonic quantum information-processing applications.