Electrically driven plasmonic light emitters strongly coupled to excitons and dielectric resonators

William Marsh Rice University, Houston TX

Investigators

Abstract

Extremely small light emitting devices are of potential use in next-generation computing and communications technologies. Two metal electrodes separated by an atomic-scale gap can function as both an electrical device and a nanoscale light source. When a current is driven across the nanogap, the electrons that “tunnel” from one electrode to the other can excite collective motions of the electrons, called plasmons, in the electrodes. Energy from successive electrons can build up in the plasmons and the electrodes, leading to a steady-state population of electrons with an effective temperature so high that they glow in the visible range. If the nanogap is very close to materials with optical resonances in that same energy range, then the light emission can be strongly modified, as energy is transferred back and forth between the metal and the optical materials. The PI proposes to examine light emission in two such coupled systems: 2D materials that act as semiconductors and have the kind of optical transitions in light emitting diodes; and special patterned insulators (cavities) that are designed to trap light at specific energies. The goals are to maximize the strength of the plasmon-material energy transfer, to examine the effect on light emission of electrically tuning the semiconductor and having very sharp cavity resonances, to create light emitting devices of this type that function stably at room temperature, and to count individual emitted photons to search for quantum effects in the light emission. Results will be presented through publications, conference talks, and accessible writing by the PI on his blog. This project will support the professional development and research training of graduate students and undergraduate researchers, contributing to a skilled technological workforce. The PI will participate in Rice efforts incorporating K12 teachers and will continue public outreach to lifelong learners through the Glasscock School of Continuing Studies. The PI’s group has demonstrated that nanoscale plasmonic tunnel junctions can emit light at energies above the applied electrical bias in an electroluminescent process based on the plasmon-assisted generation and plasmon-enhanced recombination of a steady-state population of hot carriers. In nanogaps coupled to 2D semiconductors, the electroluminescence shows peak splittings indicative of strong plasmon/exciton coupling, showing that these devices are electrically driven “plexcitonic” emitters. The PI proposes an integrated research and education program to quantify and maximize these effects. Goals include maximizing the plasmon/exciton coupling in devices incorporating gate-tunable transition metal dichalcogenides; demonstrating electroluminescence in plasmonic nanogaps strongly coupled to photonic crystal dielectric cavities; implementing such junctions in plasmonic materials that allow room temperature operation; and using photon counting statistics to examine photon bunching/antibunching, to better understand emission mechanisms in these polaritonic structures. The PI’s team of graduate and undergraduate researchers will collaborate with theorists in modeling of these systems, enabling critical feedback for optimization of device structures. Results will be presented through publications, conference talks, and accessible writing by the PI on his blog. This project will support the professional development and research training of graduate students and undergraduate researchers, contributing to a skilled technological workforce. The PI will participate in Rice efforts incorporating K12 teachers and will continue public outreach to lifelong learners through the Glasscock School of Continuing Studies. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.