Electrically Driven Optical Antennas Based On Tunnel Junctions

Optical antennas are an emerging concept in optics,analogous to the radiowave and microwave antennas,which could manipulate the light beam at the subwavelength scale.In optical frequency,it can work as the transducers between the free radiation and localized electromagnetic energy.Now,researches of optical antennas have been attracted widely attentions,including:detecting,sensing,spectral analysis and data encoding.An outstanding problem in this region is the development of electrically driven optical antennas(EDOA),which need choice a suitable driving source.Recently,researchers found that the tunneling electrons,pass through the barrier between the adjacent metals,could drive the EDOA,which provides a new subwavelength electro-optical elements.The response time of the traditional light emitting diodes is decided by the spontaneous recombination rate of electron-hole pairs.The operating peed of EDOA is only limited by the tunneling time of electrons(?1 fs).Ultrafast response speed and subwavelength device size make the EDOA suitably work as the ultrafast electro-optical devices in the nanoscale.In recent years,this field has achieved great developments in the stability of devices,improvement of external quantum efficiency and on-chip integrated designs.But,there are still many problems,such as the lack of optimization of emission spectral,few works have paid attention to the wavelength tunable EDOA,and the fabrication method of high efficiency EDOA consisting of nanoparticles is difficult and low throughput.So,the study of the optimization of emission spectral and high efficiency manufacturing technology of EDOA will have the positive significance for the nanophotonics.The article mainly focused on the tunneling electrons driven cavity plasmons,the wavelength tunable EDOA and the controllable design of EDOA based on template dielectrophoretic trapping.Specifically,the article mainly includes three aspects:First,we study the‘silver nanowire-molecular insulator-gold nanostripe'nanocavity structures.At sufficiently high bias,tunneling electrons will pass through the barrier and excite the cavity plasmon resonance,then generate photons by the radiation of nanowires.To the best of our knowledge,our work is the first time to realize the simultaneous excitation of multiple cavity plasmons by utilizing the large diameter nanowires,and observe multiple separated emission peaks.We can clearly distinguish the corresponding modes of each resonance peaks through numerical simulations.The minimum of the full-width of at half-maximum of emission peaks from cavity plasmons can reach 27 nm,which is only one-third the previously results.At the same time,the optimization direction of the electron-photon conversion efficiency of the source has also been discussion.Second,we demonstrate the wavelength tunable EDOA by adjusting the diameter of silver nanowires,which is based on the sensitive properties of cavity plasmons.The linearly shift speed of the lower-order mode can reach 2.5 nm spectral red shift for 1 nm diameter increasing.Furthermore,the number of resonance mode in the cavity is also limited by the diameter of nanowires,and it will appear new high energy peaks in the emission spectral by using the large size cavity.In the experiment,the number and position of luminescence peaks of EDOA can be adjusted at the same time.Third,high efficiency fabrication of nanoparticle device is presented by combining the high-accuracy template and dielectrophoretic trapping method.The number,orientation and relative position of nanoparticles on the electrodes are decided by the size of template.In our experiments,the tunneling electrons pass through the tunnel barrier at a point-contact area which can efficiently excite the plasmon resonance,and will be benefit to improve the quantum efficiency.The external quantum efficiency of single nanoparticle source is 2.5×10^-4,which is several orders of magnitude higher than the plane antennas sources.In addition,our devices can operate stably at the room temperature and ambient condition.Finally,we shown the electrically driven dimer and trimer source with different orientations.