The Study Of 850nm Vertical Coupled High-speed Photodetectors

With the increasing amount of network data,the rise of data center,and the development of supercomputers,the short-range interconnection has put forward higher requirements.Due to the large crosstalk and high transmission loss,the traditional copper wire connection cannot meet the requirements of high-speed signal transmission,so optical interconnection becomes a new short-distance interconnection solution.In the 850 nm short-range interconnection band,the mature high-speed VCSEL laser and multimode fiber transmission mode put forward higher requirements for the docking end performance.We start with silicon-based materials,and study the photodetectors with high speed,high response and low dark current,which can meet the needs of short-range interconnection.The coplanar interdigital photodetector structure of the surface grating is proposed,and the factors that affect the frequency bandwidth and quantum efficiency of the photodetector are studied.In the experiment,a high-speed detector meeting the requirements of optical interconnection bandwidth is made,and an effective attempt is made to improve the response.The specific work is as follows:The plane interdigital structure is used in the SOI material of 220 nm top layer silicon to achieve high-speed performance.At the same time,the Bragg grating is designed on the surface.By using the diffraction effect of the grating,the vertical absorption is changed to horizontal absorption to improve the response.In this paper,the optical design,the calculation of surface Bragg grating parameters,FDTD solution simulation software to optimize the period,duty cycle,etching depth,cover thickness and other parameters,the results show that the external quantum efficiency can reach77.3%,which is 11 times of the device without grating.Electrical simulation analyzes the capacitance and electric field characteristics of interdigital structure.After that,the process design of coplanar interdigital high-speed detector and the actual chip are carried out,and the IV characteristics,3d B bandwidth and forward on resistance of the device are tested and analyzed.The data shows that the dark current of all devices is lower than 40p A under-10V bias,the response of device with 2300?m~2 area is 3.4m A/w,3d B bandwidth is 14.1GHz,the response of device with 4300?m~2 area is 5.1m A/w,3d B bandwidth is 7.9 GHz.The forward on resistance is composed of two parts:ohmic contact resistance and interdigital resistance.According to the device structure and test results,the high-speed transit time model and RC equivalent circuit model are established respectively.The relationship between 3dB bandwidth and interdigital distance of the device is calculated and analyzed.The actual test data and theoretical value fit well.Finally,a surface Bragg grating was fabricated on the basis of coplanar finger detector,and the difference in the responsiveness of grating devices with and without grating devices was measured and analyzed.The responsiveness of grating devices increased by 20 times and 9.51 times respectively under zero bias and-30v bias.In addition,we made three different types of gratings,among which the longitudinal gratings perpendicular to the doping direction of the finger and the longitudinal spacing gratings had little effect on the bandwidth.