Design And Simulation Of Waveguide Ge/Si Avalanche Photodiode

With the rapid development of optical fiber communication and quantum communication technology,the waveguide type Ge/Si avalanche photodiode(APD)has become a research hotspot due to its high degree of integration.However,the traditional single-mode or multi-mode waveguide APD coupling efficiency is relatively low,which greatly limits the ability of light absorption of the waveguide type APD.Therefore,how to further improve the light absorption and 3dB bandwidth of the waveguide type Ge/Si APD and reduce the dark current,it has become a major hot point in domestic and international research.This article mainly focuses on the structural design and optimization of the waveguide-type Ge/Si APD.First,Silvaco software was used to design and simulate the traditional Ge/Si APD.A typical simulation model of Ge/Si APD(Separate Absorption Charge Multiplication,SACM)with separate absorption,charge,and multiplication regions was established,and its performance parameters such as dark current,photocurrent,responsivity,and 3dB bandwidth were analyzed and studied.In addition,the influence of the thickness of the Ge absorption layer on the light absorption capacity and bandwidth of the APD was also studied.On this basis,the SiGe buffer layer was substituted for Si material as the charge layer to study the influence of the SiGe buffer layer on the dark current of the device.The above research has laid a theoretical foundation for the design and optimization of the waveguide-type Ge/Si APD.Then,the design and modeling of waveguide-type Ge/Si APDS were carried out using Ansys Lumerical software.The designed rectangular waveguide Ge/Si APD uses the SOI substrate with an absorption layer of 10?m in length and 5?m in width.When the light wavelength increases from 1.31?m to 1.55?m,the light absorption of APD decreases from90%to 42%.Under the irradiation of the light source with the wavelength of 1.31?m and the optical power of-30dBm,when the reverse bias voltage is 22V,the responsivity of the waveguide type Ge/Si APD is 1.75A/W,and the 3dB bandwidth is 9.8GHz.Finally,in order to further improve the light absorption capacity of the waveguide type Ge/Si APD,this paper introduces the Bragg reflector structure to carry out the design and optimization of the waveguide type Ge/Si APD.Among them,the dielectric materials of the Bragg reflector are Si and SiO₂,and their thicknesses are 0.11?m and 0.27?m at the wavelength of 1.55?m,and0.09?m and 0.22?m at the wavelength of 1.31?m,respectively.The effect of the Bragg reflector period on the light absorption of the waveguide type Ge/Si APD was studied by simulation.When the Bragg reflector period is 0,1,2,3,4,the results show that the light absorption at the wavelength of 1.55?m is 42%,64%,67%,67%and 67%,respectively,and the light absorption at 1.31?m wavelength is 90%,96.2%,97.5%,97.75%and 97.75%respectively.Compared with waveguide type APD without Bragg reflector,the light absorption increased by 25%and 7.75%respectively.The optimizedBragg reflector waveguide type APD is illuminated by the light source with wavelengths of 1.55?m and1.31?m and the optical power of-30dBm.When the reverse bias voltage is 22V,the 3dB bandwidth of the APD is 9.8GHz,and the dark current corresponds to 0.9Vbr is 7.75×10^-9A,and the responsivity is 1.5A/W and 1.89A/W,while the responsivity of the waveguide type APD without Bragg reflector is 1A/W and 1.75A/W,respectively,indicating the introduction of Bragg reflector greatly improves the responsivity of the waveguide type Ge/Si APD at the wavelength of 1.55?m.