Structure Optimization And Characteristic Analysis Of High-Performance Photodetector For Optical Communication

With the development of information technology,the requirements for large-capacity and long-distance transmission are more and more urgent.Optical fiber communication has been rapidly developed with its advantages of small transmission loss,large bandwidth and good anti-electromagnetic interference performance.As one of the core components of optical fiber communication systems,people put forward higher requirements on photodetectors:higher quantum efficiency,faster response speed,better linear performance and so on.Partially depleted absorber photodetector(PDA-PD)has good linear performance,while dual-depletion region photodetector(DDR-PD)reduces the capacitance,thereby increasing the high-speed performance of the photodetector.In this dissertation,PDA-PD and DDR-PD are studied separately,then the combination of the two structure is optimized and simulated.The simulation results are analyzed theoretically.The integration of the traditional PIN-PD with the grating with reflection convergence effect can improve the quantum efficiency of the PD.The structure is optimized and tested by experiments.The main work and innovations of this dissertation are listed as follows:1.In order to improve the linear performance of the photodetector,the structure of the PDA photodetector is optimized,and the simulation results are theoretically analyzed.When the device has a diameter of 20?m and a reverse bias voltage of 3 V is applied,the saturation output current of the PDA-PD is increased from 8mA to 10mA compared with PIN-PD,and the bandwidth efficiency product(BWE)is increased from 11.2GHz to 18.17GHz,which improved 66.2%.The corresponding bandwidth is increased from 23.27GHz to 27.37GHz.At this time,the thickness of the depletion absorption layer of the PDA-PD was 500 nm,and the thickness of the partially depleted absorption layer was 700 nm.2.In order to improve the high-speed response performance of the photodetector,the structure of the DDR photodetector is optimized.The simulation results are explained from the aspects of electric field and carrier velocity.The applicable conditions of the DDR structure are also analyzed.With a device diameter of 20p.m and a reverse bias voltage of 3 V,when the thickness of the absorption layer is 500 nm and the thickness of the drift enhancement layer is 400 nm,the BWE of DDR-PD is maximized to 14.1 GHz,the corresponding bandwidth reaches 37.3GHz.Compared with the optimal BWE of PIN-PD,DDR-PD has increased by 25.9%.3.In order to further improve the perfoance of the photodetector,the PDA structure and the DDR structure are combined.This combined structure can improve the linear performance and high-speed response performance simultaneously.When the partially depleted absorption layer thickness is 550nm,the thickness of the absorption layer is 350nm,and the thickness of the drift enhancement layer is 450nm,the quantum efficiency of the photodetector reaches 56.6%,and the 3dB bandwidth reaches 39.7GHz.The optimal BWE is 22.47 GHz,which is twice the best BWE for a normal PIN-PD.4.In order to improve the quantum efficiency of the PIN-PD,the structure of PIN-PD integrated with subwavelength grating with reflection convergence effect is studied.The diameter of the photodetector is 40?m and the reverse bias voltage is 3 V.When the device reflectance is 99%,the optimized integrated structure has a quantum efficiency of 55.5%and a bandwidth of 18.3GHz,which is 53.7%higher than the 36.1%quantum efficiency of the conventional PIN structure.The best BWE is improved from 6.54GHz to 10.17GHz.5.Through the simulations on different input optical power,different light input directions and different p-contact electrodes,the factors affecting the performance of the photodetector are explored to obtain the best performance.According to the electric field distribution,potential distribution and carrier velocity of the photodetector,the simulation results are theoretically analyzed and explained.The simulation results show that the bandwidth of PDA-DDR-PD decreases with the increase of input optical power(or output current).For the PDA-DDR-PD structure optimized in this dissertation,the incident optical intensity should be less than 2900W/cm2.In addition,it is found that the photodetector using a full-covered p-contact electrode is better than using the ring-covered p-contact electrode.6.The PIN-PD integrated with subwavelength gratings are experimentally measured,and the effects of different output currents,different p-contact electrodes and light-input directions on the performance of photodetector are measured.According to the experimental results,the simulation results are able to be verified.