skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Efficient light generation from enhanced inelastic electron tunnelling
Light emission from biased tunnel junctions has recently gained much attention owing to its unique potential to create ultracompact optical sources with terahertz modulation bandwidth1,2,3,4,5. The emission originates from an inelastic electron tunnelling process in which electronic energy is transferred to surface plasmon polaritons and subsequently converted to radiation photons by an optical antenna. Because most of the electrons tunnel elastically, the emission efficiency is typically about 10−5–10−4. Here, we demonstrate efficient light generation from enhanced inelastic tunnelling using nanocrystals assembled into metal–insulator–metal junctions. The colour of the emitted light is determined by the optical antenna and thus can be tuned by the geometry of the junction structures. The efficiency of far-field free-space light generation reaches ~2%, showing an improvement of two orders of magnitude over previous work3,4. This brings on-chip ultrafast and ultracompact light sources one step closer to reality.  more » « less
Award ID(s):
1636356
PAR ID:
10120631
Author(s) / Creator(s):
; ; ; ; ; ; ;
Date Published:
Journal Name:
Nature photonics
Volume:
12
ISSN:
1749-4885
Page Range / eLocation ID:
485-488
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, The Journal of Chemical Physics)
    Over the last century, quantum theories have revolutionized our understanding of material properties. One of the most striking quantum phenomena occurring in heterogeneous media is the quantum tunneling effect, where carriers can tunnel through potential barriers even if the barrier height exceeds the carrier energy. Interestingly, the tunneling process can be accompanied by the absorption or emission of light. In most tunneling junctions made of noble metal electrodes, these optical phenomena are governed by plasmonic modes, i.e., light-driven collective oscillations of surface electrons. In the emission process, plasmon excitation via inelastic tunneling electrons can improve the efficiency of photon generation, resulting in bright nanoscale optical sources. On the other hand, the incident light can affect the tunneling behavior of plasmonic junctions as well, leading to phenomena such as optical rectification and induced photocurrent. Thus, plasmonic tunneling junctions provide a rich platform for investigating light–matter interactions, paving the way for various applications, including nanoscale light sources, sensors, and chemical reactors. In this paper, we will introduce recent research progress and promising applications based on plasmonic tunneling junctions. 
    more » « less
  2. ; ; ; (, Optics Express)
    Nanoscale plasmonic gaps are useful structures both electrically, for creating quantum tunnel junctions, and optically, for confining light. Inelastic tunneling of electrons in a tunnel junction is an attractive source of light due to the ultrafast response rate granted by the tunneling time of electrons in the system as well as the compact dimensions. A main hurdle for these light emitting tunnel junctions, however, is their low external efficiency given by both low electron-to-plasmon conversion as well as low plasmon-to-photon conversion. Inversely, coupling light into a nanogap for high confinement and field enhancement can be difficult due to the size mismatches involved. We show a 3 nm gap metal-insulator-metal plasmonic tunnel junction evanescently coupled to the fundamental TE mode of a standard silicon waveguide in a tapered directional coupler configuration with a transmission efficiency of 54.8% atλ =1.55μm and a 3-dB coupling bandwidth of 705 nm. In the inverse configuration, we show an electric field enhancement of |E|/|E0| ≈120 within a plasmonic tunnel junction in the technologically important optical telecommunications band. 
    more » « less
  3. ; ; ; ; (, EMC)
    Ultra-violet light emitting diodes (UV-LEDs) and lasers based on the III-Nitride material system are very promising since they enable compact, safe, and efficient solid-state sources of UV light for a range of applications. The primary challenges for UV LEDs are related to the poor conductivity of p-AlGaN layers and the low light extraction efficiency of LED structures. Tunnel junction-based UV LEDs provide a distinct and unique pathway to eliminate several challenges associated with UV LEDs1-4. In this work, we present for the first time, a reversed-polarization (p-down) AlGaN based UV-LED utilizing bottom tunnel junction (BTJ) design. We show that compositional grading enables us to achieve the lowest reported voltage drop of 1.1 V at 20 A/cm2 among transparent AlGaN based tunnel junctions at this Al-composition. Compared to conventional LED design, a p-down structure offers lower voltage drop because the depletion barrier for both holes and electrons is lower due to polarization fields aligning with the depletion field. Furthermore, the bottom tunnel junction also allows us to use polarization grading to realize better p- and n-type doping to improve tunneling transport. The epitaxial structure of the UV-LED was grown by plasma-assisted molecular beam epitaxy (PAMBE) on metal-organic chemical vapor deposition (MOCVD)-grown n-type Al0.3Ga0.7N templates. The transparent TJ was grown using graded n++-Al0.3Ga0.7N→ n++-Al0.4Ga0.6N (Si=3×1020 cm-3) and graded p++-Al0.4Ga0.6N →p++-Al0.3Ga0.7N (Mg=1×1020 cm-3) to take advantage of induced 3D polarization charges. The high number of charges at the tunnel junction region leads to lower depletion width and efficient hole injection to the p-type layer. The UV LED active region consists of three 2.5 nm Al0.2Ga0.8N quantum wells and 7 nm Al0.3Ga0.6N quantum barriers followed by 12 nm of p- Al0.46Ga0.64N electron blocking layer (EBL). The active region was grown on top of the tunnel junction. A similar LED with p-up configuration was also grown to compare the electrical performance. The surface morphology examined by atomic force microscopy (AFM) shows smooth growth features with a surface roughness of 1.9 nm. The dendritic features on the surface are characteristic of high Si doping on the surface. The composition of each layer was extracted from the scan by high resolution x-ray diffraction (HR-XRD). The electrical characteristics of a device show a voltage drop of 4.9 V at 20 A/cm2, which corresponds to a tunnel junction voltage drop of ~ 1.1 V. This is the best lowest voltage for transparent 30% AlGaN tunnel junctions to-date and is comparable with the lowest voltage drop reported previously on non-transparent (InGaN-based) tunnel junctions at similar Al mole fraction AlGaN. On-wafer electroluminescence measurements on patterned light-emitting diodes showed single peak emission wavelength of 325 nm at 100 A/cm2 which corresponds to Al0.2Ga0.8N, confirming that efficient hole injection was achieved within the structure. The device exhibits a wavelength shift from 330 nm to 325 nm with increasing current densities from 10A/cm2 to 100A/cm2. In summary, we have demonstrated a fully transparent bottom AlGaN homojunction tunnel junction that enables p-down reversed polarization ultraviolet light emitting diodes, and has very low voltage drop at the tunnel junction. This work could enable new flexibility in the design of future III-Nitride ultraviolet LEDs and lasers. 
    more » « less
  4. ; ; ; ; (, SPIE Conference Proceeding)
    Strassburg, Martin; Kim, Jong Kyu; Krames, Michael R. (Ed.)
    AlGaN-based ultra-violet light emitting diodes (UV LEDs) are promising for a range of applications, including water purification, air disinfection and medical sensing. However, widespread adoption of UV LEDs is limited by the poor device efficiency. This has been attributed to the strong internal light absorption and poor electrical injection efficiency for the conventional UV LED structures, which typically use an absorbing p-GaN layer for p-type contact. Recent development of ultra-wide banggap AlGaN tunnel junctions enabled a novel UV LED design with the absence of the absorbing p-GaN contact layer. In this presentation, we will discuss recent progress of the AlGaN tunnel junctions and the development of tunnel junction-based UV LEDs, and discuss the challenges and future perspectives for the realization of high power, high efficiency UV LEDs. 
    more » « less
  5. ; ; ; (, Nanophotonics)
    Plasmonic modes confined to metallic nanostructures at the atomic and molecular scale push the boundaries of light–matter interactions. Within these extreme plasmonic structures of ultrathin nanogaps, coupled nanoparticles, and tunnelling junctions, new physical phenomena arise when plasmon resonances couple to electronic, exitonic, or vibrational excitations, as well as the efficient generation of non-radiative hot carriers. This review surveys the latest experimental and theoretical advances in the regime of extreme nano-plasmonics, with an emphasis on plasmon-induced hot carriers, strong coupling effects, and electrically driven processes at the molecular scale. We will also highlight related nanophotonic and optoelectronic applications including plasmon-enhanced molecular light sources, photocatalysis, photodetection, and strong coupling with low dimensional materials. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email