Research On High Saturation And Broadband Uni-Traveling-Carrier Photodetector

Photodetectors are the key components of radio-over-fiber systems,and the high speed and saturation output performance of photodetectors play an important role in the transmission rate and quality of communication systems.Because of the excellent high speed and high saturation performance,uni-traveling-carrier photodetectors(UTC-PDs)have become a hot research object in the field of photodetectors.To achieve the performance of high speed and high power in future communications,this paper focuses on the high saturation and broadband uni-traveling-carrier photodetector to research.By designing the epitaxial layer structure of the uni-traveling-carrier photodetector,the problem that the bandwidth is limited by the electron transit time and the saturation current is limited by the space charge effect is solved,so that the unitraveling-carrier photodetector can meet the performance requirements of broadband and high saturation.The specific innovation work is as follows:1.Based on the study of the relationship between the build-in electric field and the high-speed performance,a new doping scheme is proposed in this paper.Using linear doping distribution in the absorption layer,the exponential growth electric field can be introduced inside the device and the electron transit time can be shorten,thus the high-speed performance of the UTC-PD can be improved.Simulation results show that the 3dB bandwidth of the optimized UTC-PD is two times higher than that of conventional UTC-PD with uniform doping.2.Based on the study of the relationship between the epitaxial layer structure and the high speed high saturation performance,a modified high saturation and broadband UTC-PD structure is proposed in this paper,in which using high doping thick cliff layer and space layer to reduce the effect of space charge effect,and the thickness and distribution of linear doping concentration of absorption layer and collection layer are optimized,thus the electron transit time is shorten and the performance of broadband high saturation is achieved.The simulation results show that the improved UTC-PD device can achieve a bandwidth of 146 GHz and a saturation current of 348 mA,which can be used in high-speed optical fiber communication systems.3.A novel double-cliff hourglass UTC-PD structure is proposed to solve the problem of the interaction between the electron transit time and RC time constant in bandwidth,and to achieve better broadband high saturation performance without sacrificing responsivity,reaching the subterahertz bandwidth.The simulation results show that the dual-cliff hourglass UTC-PD can achieve a high bandwidth of 223 GHz and a high saturation output power of 30 dBm,which is 6.5%higher than the conventional UTC-PD with a bandwidth saturation current product,and can be used in sub-terahertz communications.