Fabrication Of Plasmonic Nanogap And Its Application In Silicon-based Near-infrared Photodetection

Surface plasmon(SP)refers to the electromagnetic(EM)resonance generated by the coupling of incident photons and freely oscillating electrons on the metal surface.In the past few decades,SP has been widely studied and applied in biology,photochemistry,energy and other fields due to its excellent capabilities of tailoring spectral features and manipulation the EM-field in spatial domain.Typically,the photon absorption in metal nano-systems is considered to be a parasitic loss mechanism,which eventually dissipates its energy as heat.How to efficiently harvest this ‘metallic loss’ and convert it to electricity power or the catalytic stimulus for reactions has become a hot topic in the current research of plasmonic optics.Most recently,this leads to innovations encompass both the emerging device and mechanism in the area of photodetection and photocatalysis.For example,the generated hot carriers in metals due to photon absorption can be converted to photocurrent signal through electron tunneling and thermal emission.As a new strategy for realizing optoelectronic conversion,it holds great potential for photodetection application.As an effective mean for enhancing light-matter-interaction(LMI),the plasmonic nanogap enables extreme strong EM-field localization and ultra-small mode volume.Regarding on the its application to optoelectronic conversion,the plasmonic nanogap allows for effective manipulation of photon absorption in spectral and spatial domains,resulting in enhanced hot carrier properties in terms of generation,transport and emission.Therefore,higher quantum efficiency can be achieved in the nanogap configuration.However,many technical challenges still remain to fabrication the plasmonic nanogap in the cost-effective and scalable manner.To this end,this paper presents several different fabrication approaches for realizing plasmonic nanogap,including electron beam lithography,self-assembled nanosphere template,selforganization via thin film thermal dewetting and plasmon-assisted chemical growth.We have successfully fabricated plasmonic nano-bowties,nano-triangles and nanoislands structures.The fabricated sub-wavelengths metallic structures can couple with free space light and leads to large EM-field localization around nanogaps through the excitation of localized surface plasmon resonance.Moreover,spectral features with desired narrow-band or broadband resonances can be realized by simply tailoring the size and morphology of the nanogaps.Then,we propose and design a plasmonic hot carrier photoconductive device on silicon platform using the random nano-island structure.Relying on the randomly and densely distributed hot spots,efficient and broadband photon harvesting as well as improved quantum efficiency of optoelectronic conversion were demonstrated beyond the silicon absorption cut-off wavelength.In addition,the back-to-back Schottky diode configuration with the multi-finger metal-semiconductormetal(MSM)electrodes differs significantly from the reported photovoltaic type devices as it can offer high photoconductive gain.Our experimental results demonstrate that with a proper external biasing voltage,the hot carrier mediated photocurrent responsivity of the proposed device is as high as 5.12 A/W at the wavelength of 1310nm.