Research On The Characteristics Of High-Speed And Large-Photosensitive-Surface Photodetector In Space Optical Communication

Photodetector is the key component applied to the field of Space Optical Communication.With the rapid development of integrated optoelectronics technology in this field,the characteristics of high-speed and large-photosensitive-surface of the detector are urgently demanded.The Uni-Traveling-Carrier Photodetector(UTC-PD)uses the electron as the active carrier and has the high-speed characteristic with the help of built-in electric field.Besides,it overcomes the influence of Space Charge Effect effectively and achieves the large-photosensitive-surface characteristic advantageously.The UTC-PD has great advantages in practical application.Based on the working principle of the UTC-PD,the output response of the detector is derived and detailed theoretical analysis about the influencing factors is carried.Different structures are analyzed by simulation and the the characteristics of high-speed and large-photosensitive-surface of the detector are studied in this thesis.Main research content in this thesis is as follows:1.The characteristic parameters of the detector are analyzed.The main influencing factors of the 3 d B bandwidth are determined and they include carrier's transit time and junction capacitance;The output response of the UTC-PD is derived by AC small-signal analysis method.The simulation tool MATLAB is used to make quantitative analysis on the output response and the influence of potential energy gradient??,absorption layer's thickness W_A and collecting layer's thickness W_c on bandwidth is specifically studied.The analysis results show that the built-in electric field could promote the carrier's motion and reduce carrier's transit time.The size of the epitaxial layer would make influence on the carrier's transit time and junction capacitance,and make further influence on the output response.2.The structure of the UTC-PD is simulated by ATLAS of commercial Silvaco.The electrode's structure is modified to transfer the peak region of photogeneration rate and the electric field intensity in the absorption region is increased,which greatly improves the device's response capability.The designing scheme of the size of epitaxial layer,doping and material's composition is optimized,and the influence of response's change is analyzed from the micro perspective.Research results show that the response capability could be improved effectively by reducing carrier's transit time and junction capacitance.In the light of incident wavelength of 1550 nm,considering the influence of 65?impedance and 10 f F capacitance,the photosensitive surface's diameter of the structure is 10?m,and the 3 d B bandwidth exceeds 120 GHz;Contrasted with the detector's performance of predecessor's research,the results indicate that our structure has certain advantages in achieving the characteristics of high-speed and large-photosensitive-surface.In DC operating condition,characteristic parameters of detector are studied and summarized.3.The influence of the change of photosensitive surface's diameter on the response capability of the UTC-PD is studied in this thesis.The results show that 3 d B bandwidth could be improved by decreasing the thickness of absorption layer W_A in a certain range when the diameter of photosensitive surface is increased.When the diameter of photosensitive surface is 10.25?m,the maximum bandwidth could be obtained when the thickness of absorption layer is 190 nm and the maximum value is 110.64 GHz;Three kinds of parallel UTC-PD structure are simulated.Finally,the area of photosensitive surface of three detectors are 238.76?m~2,254.40?m~2 and 219.90?m~2 separately and their 3d B bandwidth exceed 45 GHz through structure design and characteristic analysis.In DC operating condition,characteristic parameters of different detectors are studied and summarized.