Highly Efficient Midinfrared On-Chip Electrical Generation of Graphene Plasmons by Inelastic Electron Tunneling Excitation

Inelastic electron tunneling provides a low-energy pathway for the excitation of surface plasmons and light emission. We theoretically investigate tunnel junctions based on metals and graphene. We show that graphene is potentially a highly efficient material for tunneling excitation of plasmons because of its narrow plasmon linewidths, strong emission, and large tunability in the midinfrared wavelength regime. Compared to gold and silver, the enhancement can be up to 10 times for similar wavelengths and up to 5 orders at their respective plasmon operating wavelengths. Tunneling excitation of graphene plasmons promises an efficient technology for on-chip electrical generation and manipulation of plasmons for graphene-based optoelectronics and nanophotonic integrated circuits.Comment: 12 pages, 7 figure

Graphene-based thermionic-thermoradiative solar cells: Concept, efficiency limit, and optimum design

Abstract(#br)Solar energy conversion to electricity usually adopts two main methods: photovoltaic and solar-thermal power generation. Here, graphene-based thermionic-thermoradiative solar cells are expanded to include photovoltaics based on thermionic-thermoradiative converters, hybrid concept, efficiency limit, and optimum design. For realistic and practical design, a comprehensive and consistent model is formulated to include effects of thermal coupling between the absorbers, space-charge effect, non-radiative recombination, and various irreversible energy losses. By combining thermionic emission and thermoradiative mechanisms, thermionic-thermoradiative solar cells make use of electron and photon fluxes simultaneously to efficiently convert solar radiation to electricity, and thus enable a significant improvement in terms of heat utilization and conversion efficiency. Based on the calculated results, optimum choices of materials and the parametric design strategies of the system are determined. The findings predict a high solar-to-electricity efficiency of 0.225 in using a graphene-caesiated tungsten graphene-based thermionic energy converter and an Aluminium-32 gallium-48 arsenide-based thermoradiative cell under 800 sun irradiance. This work also demonstrates the importance of recycling waste heat for performance optimization and opens up new avenues to boost the overall conversion efficiency of such systems

Space–charge limited current in nanodiodes: Ballistic, collisional, and dynamical effects

This Perspective reviews the fundamental physics of space–charge interactions that are important in various media: vacuum gap, air gap, liquids, and solids including quantum materials. It outlines the critical and recent developments since a previous review paper on diode physics [Zhang et al. Appl. Phys. Rev. 4, 011304 (2017)] with particular emphasis on various theoretical aspects of the space–charge limited current (SCLC) model: physics at the nano-scale, time-dependent, and transient behaviors; higher-dimensional models; and transitions between electron emission mechanisms and material properties. While many studies focus on steady-state SCLC, the increasing importance of fast-rise time electric pulses, high frequency microwave and terahertz sources, and ultrafast lasers has motivated theoretical investigations in time-dependent SCLC. We particularly focus on recent studies in discrete particle effects, temporal phenomena, time-dependent photoemission to SCLC, and AC beam loading. Due to the reduction in the physical size and complicated geometries, we report recent studies in multi-dimensional SCLC, including finite particle effects, protrusive SCLC, novel techniques for exotic geometries, and fractional models. Due to the importance of using SCLC models in determining the mobility of organic materials, this paper shows the transition of the SCLC model between classical bulk solids and recent two-dimensional (2D) Dirac materials. Next, we describe some selected applications of SCLC in nanodiodes, including nanoscale vacuum-channel transistors, microplasma transistors, thermionic energy converters, and multipactor. Finally, we conclude by highlighting future directions in theoretical modeling and applications of SCLC.Peer-reviewed (ritrýnd grein