Research On Mechanism Of Shortwave Infrared Enhancement Based On Optical Nano-antenna

Short wave infrared InGaAs detectors have been widely used in aerospace and imaging detection applications,due to its high stability,low dark current and high detection rate at high operating temperatures.With the continuous improvement of detection requirements,InGaAs detectors are also developing in the direction of reducing the photosensitive cell area and expanding the size of the focal plane.However,the continuous reduction of the photodetector area of the detector will reduce the energy of the incident light that can be effectively collected,reduce the signal-to-noise ratio,and increase the detection difficulty.It is very urgent to introduce new structures to enhance the absorption of incident light.The light absorption performance of the detector can be enhanced by nano-antenna with light scattering and surface local field enhancement effects.In this paper,an integrated nano-antenna structure is proposed to fully collect the incident light.Two types of nano-antenna structures,nano-ball and nano-block,have been designed.The performance of the nano-antenna structure has been simulated.The enhanced transmission and polarization characteristics of nanoantennas have been investigated.The preparation process of the nano-ball structure has been explored.The transmittance enhancement of nano-antenna was verified.A method for preparing a sub-wavelength metal grating was studied.An electron beam lithography method was used to prepare a grating on a SiO₂/InP substrate and a backilluminated device.The performance of InGaAs detectors with integrated metal gratings was tested.A systematic theoretical study was conducted on the light transmission performance of the two metal nano-antennas designed in 1.0-1.7 ?m by FDTD Solutions.Firstly,the effects of different metal materials,metal ball radii and cycles on the transmission performance in the SiO₂/Metal ball/InP structure were investigated.It was found that adding a layer of SiO₂ on the metal ball array can simultaneously stimulate the SPP mode as well as the LSP mode.At the same time a transparent effect was produced through the regulation of the thickness of SiO₂,thereby significantly enhancing the transmittance near 1 ?m.After that,the effects of different metal materials,the length of the bottom edge of the metal block,the height of the metal block,the period,and the thickness of the SiO₂ in the Metal block/SiO₂/InP structure were studied.Taking into consideration the process window of each nano-antenna comprehensively,the structural parameters of SiO₂/Metal ball/InP structure are fixed to be: Ag material,radius of metal ball are between 190 nm to 200 nm,period is between 700 nm to 900 nm,thickness of SiO₂ = 500 nm.The structural parameters of Metal block/SiO₂/InP structure are fixed to be: Au material,side length of metal block is between 140 nm to 180 nm,height of metal block is between 80 to 100 nm,period is between 360 nm to 400 nm,thickness of SiO₂ is between 90 nm to 110 nm.The preparation process of nano-antenna was designed according to the results of theoretical simulation,and the key process parameters of preparing SiO₂/Metal ball/InP structure nano-antenna were preliminarily explored.The SiO₂/Metal ball/InP structure nano-antenna sample was prepared by ultrasonic dispersive deposition method.The effect of deposition time on the arrangement of Ag particles was investigated.It was found that the deposition time was suitable between 2 h and 3 h.The samples were tested before and after the SiO₂ film was grown.It was found that the Metal ball/InP structure nano-antenna withut SiO₂ film did not substantially enhance the light transmittance near 1 ?m.The transmittance increases with the wavelength of incident light.After the growth of SiO₂ film,the transmittance near 1?m was significantly improved,and the transmittance in 1-l.7?m was relatively enhanced.The experimental results are in good agreement with the theoretical simulation results,which verifies the reliability of the theoretical simulation.The integration process of sub-wavelength metal gratings and back-illuminated 30 ?m pixel pitch InGaAs line devices was explored.The preparation process of the subwavelength metallic grating based on surface plasmon effect was explored.After metallization,electron beam lithography,metal evaporation,stripping and other processes,a subwavelength Al grating is fabricated on a SiO₂/InP substrate.The measured width is about 205 nm,the period is about 409 nm,and the duty cycle is about 50%,which is consistent with the designed structure.The gratings were fabricated on back-illuminated InGaAs detectors.In order to solve the lithography alignment problem of back-illuminated devices,gold markings were introduced.The prepared grating is a 2×2 array,arranged at four angles of 0°,45°,90°,and 135°,respectively.A clear fourdirectional wire grid structure was obtained.The performance of the InGaAs detector with integrated metal grating was tested.The test results showed that the device has obvious polarization detection characteristics and the extinction ratio was 11 at 1310 nm,higher than the same type of device performance reported in foreign literature.