Research Of High Speed UTC Photodiodes In Optical Communication System

As a key component in optical communication system,the optimization of photodetector's high-speed performance plays a vital role in the future development of the whole optical communication system.In Uni-Traveling-Carrier photodetector(UTC-PD),Electron as the single carrier to transmission,which greatly reduces the carrier's transit time and effectively reduces the space charge effect.it is now one of the research hotspots in the field of high-speed photoelectronic devices.This dissertation starts with the optical field distribution of the incident beam of UTC photodetector and the lateral Gaussian doping of the device absorption layer,focusing on the high-speed performance of photodetectors.The main research contents and innovations are as follows1.The relationship between the optical field distribution of the incident beam and the high-speed performance of UTC-PD is studied.In the study,the incident-light method is back-illuminated.When the bias is low,the device bandwidth is higher under the incident beam with uniform optical-field,but with the increase of the bias voltage,the high speed performance of the device is improved obviously by the quasi-gaussian incident beam with concentrated power.the UTC-PD with a radius of 5?m has a bandwidth of 77.91 GHz under a 2V bias,an increase of 17.23%.2.The mechanism of the influence of the light field distribution on the high-speed performance of the device under the condition of back-illuminated is mainly divided into two aspects:one is that the quasi-gaussian incident beam will cause the difference in the carrier concentration of the absorption layer in the radial direction,causing the carriers in the center area of the device to spread to the surroundings,which reduces the accumulation of carriers to a certain extent;The second is that under the quasi-gaussian incident beam,the electric field value gradually increases along the radial direction,so that the carriers in the center area of the device drift radially to the surroundings;the superposition of the two effects makes the space charge effect in the center area of the device alleviated which improves the overall high-speed performance of the device.3.Based on optical field distribution on the UTC-PD high-speed performance,a new UTC-PD structure is proposed.The absorption layer of the new structure adopts a radially graded gaussian doping scheme,which can significantly improve the electric field distribution of the absorption layer and alleviate the space charge effect.In addition,the electric field distribution of heterogeneous interface in the new UTC-PD increase to a certain extent and the overall capacitance of the device significantly decrease.With the optimization of the layer of new UTC-PD,under 1V bias,the new structure with a diameter of 5?m,when the uniform beam intensity is 4e5W/cm2,obtains a 3dB bandwidth of 88.84GHz.The bandwidth of the original UTC-PD structure is 62.81 GHz,and the 3dB bandwidth of the new structure has increased by 41.44%.4.The back-illuminated PIN-PD device was fabricated and it's performance test was finished.The results show that the 3dB bandwidth of PIN-PD with a diameter of 50?m is 5.409GHz at 3 V bias.