Roughness-coupled light emission from tunnel junctions: The role of the fast surface plasmon

Efficient Surface Plasmon Polariton Excitation and Control over Outcoupling Mechanisms in Metal–Insulator–Metal Tunneling Junctions

“…Here we show through experiments supported by theory that the MIM‐SPP mode readily outcouples via three possible outcoupling pathways of the MIM‐SPP mode: i) scattering of the MIM‐SPP to photons at the different dielectric–metal interfaces16,38–41,44,49 (Figure 1c,d, pathway 1), ii) coupling of the MIM‐SPP to bound‐SPP modes by spatial mode‐overlap and roughness‐induced momentum matching22,30,35,37,57 (Figure 1c,d, pathway 2), and iii) direct coupling of the MIM‐SPP mode to photons as well as the bound‐SPP modes at the edge of the MIM‐TJ and the adjacent waveguides14,27 (Figure 1c,d, pathway 3). By studying light emission from Al‐AlO x ‐Cr‐Au MIM‐TJs integrated into Al and Au waveguides (Figure 1b) and varying the Al and Au thickness (Figure 1c,d) we demonstrate that the MIM‐SPP mode couples to the bound‐SPP modes (Figure 1c,d), where the coupling efficiency is a function of the effective electrode thickness.…”

“…These works are accurate for smooth MIM‐TJs with no roughness but neglect to consider the role of surface roughness and coupling via pathway 2. Their argument cannot explain considerable literature that reports light emission from the MIM‐TJ area,16,21,22,26,30,37,43–46,48,49,60–62 and cannot explain the observations shown in Figure 3.…”

“…Furthermore, we demonstrate experimental control over outcoupling of the MIM‐SPP mode and the outcoupling pathways to radiative (photons) and non‐radiative (SPPs) modes. Our work shows experimental efficiencies can be further increased by exploiting surface roughness at the MIM–TJ interfaces22,29,30 which, in principle, can be extended by coupling other types of structures to junctions, such as antennas or gratings.…”

“…Therefore, in order to increase outcoupling efficiencies, momentum‐matching conditions at the metal–dielectric interfaces are required to outcouple the mode to both free space photons and to bound‐SPPs 26,35. Randomly roughened electrodes,17,22,29,30,36–42 gratings,21,43,44 and prisms,45 have been integrated into MIM‐TJs to preferentially outcouple the MIM‐SPP mode or the bound‐SPP mode(s) to photons by reducing this momentum mismatch 17,26,43–46…”

Directional launching of surface plasmon polaritons by electrically driven aperiodic groove array reflectors

“…We note that MIM-TJs are commercially available (e.g., magnetic tunnel junctions, Josephson junctions, tunnel diodes, millimeter wave detectors, or rectennas) [32][33][34][35][36] and can be scaled to subhundred nanometers [37,38]. The challenge is to outcouple the highly confined MIM SPP mode to a single interface SPP mode that propagates along a dielectric-metal interface of a plasmonic waveguide because the momentum of the MIM SPP is one order of magnitude larger than that of the single interface SPPs [39][40][41].…”