Optical Field Design And Research Of The New Type Of Silicon Photodetector

Silicon material has perfect lattice,mature technology,and can be directly integrated with CMOS readout circuit,making it an ideal detector material.However,limited by the intrinsic band gap,the absorption coefficient of silicon material at 1064 nm is～10 cm-1,resulting in low sensitivity of conventional detectors in this band.Therefore,in order to meet the development requirements of higher-performance lidar in the future and develop a highly sensitive 1064 nm silicon photodetector,it is necessary to solve the problem of low sensitivity caused by the intrinsic properties of materials and the limitations of traditional structures.This is also a "stuck neck" scientific problem that urgently needs to be overcome to promote the high-quality development of lidar,and an important challenge for the new generation of information technology.In this paper,aiming at improving the absorption efficiency of silicon photodetectors in the 1064 nm band,two methods are proposed to compensate for the low absorption coefficient of materials by increasing the length of the interaction between light and matter,and they are respectively studied.The main results are as follows:1.The structure of the guided-mode silicon photodetector is proposed.The optical transmission direction of traditional photodetectors is consistent with the direction of the electric field,resulting in the mutual restriction of the structure of the optical field and the electric field.The proposed guided mode structure solves the problem of low light absorption efficiency caused by short absorption length by decoupling the electric field and optical field direction,so that the carrier transport is not limited by the absorption length,thereby improving the responsivity.Three parts of the optical composition of the guided mode silicon photodetector,including the coupling input structure,the transmission absorption structure and the end reflection structure,are designed and optimized by simulation.By changing the spatial distribution of the refractive index to control the optical field distribution,the efficient coupling input and spatial folding of the optical field are realized,and a compact device structure is designed.Aiming at the problem of the center wavelength shift of the grating coupler caused by the process error,an"angle adjustment method" was proposed,and a coupled test platform was designed to improve the test difficulty caused by the narrow spectral range of the 1064 nm laser.The optimized grating structure period is 460 nm,the duty cycle is 0.52,and when the etching depth is 100 nm,the coupling incidence efficiency of up to 56%can be obtained at 1064 nm.And within the process error range of 10 nm,the coupling incidence efficiency can be kept above 47%by the "angle adjustment method".Finally,a device-level simulation was carried out using the PIN electrical structure,and the results showed that the structure had a responsivity of 0.51 A/W(@3 V,110 nW)at 1064 nm.2.A light absorption enhancement structure based on Mie scattering is proposed.The absorption,scattering and extinction cross-sections of subwavelength spherical particles with Mie scattering are calculated by strict analytical solution,and the contributions of different Mie resonance modes to the cross-section and the influence of the characteristic parameters of the sphere on the cross-section are analyzed.The FDTD software simulation results verify the conclusion of the analytical solution,obtain the field distribution in the sphere under different resonance modes,and calculate the characteristic size parameters required for the silicon sphere to excite different resonance modes at the 1064 nm band.The relationship between the absorptivity of the target light by the silicon Mie resonant light absorption enhancement structure on the SOI silicon substrate and the resonant sphere radius and its array arrangement is simulated and analyzed.The results show that when the silicon sphere radius is 140 nm and the arrangement When the period is 380 nm,the absorption rate of the structure at 1064 nm increases from almost 0 to 28%,which verifies the feasibility of the Mie resonance structure to improve the light absorption rate.