Research Of Novel Partially Depleted Absorber Photo-detector For Optical Communication

Under the background of today's information age,the demand for high-bandwidth of the high-speed Internet puts forward higher requirements on the communication system.The optical fiber communication system which is characterized with ultra-large bandwidth,ultra-large transmission capacity,ultra-long transmission distance and low-loss characteristics has wonderfully met these requirements and obtained huge developments.Playing an important role in completing the photoelectric signal conversion,photodetector is one of the key devices of optical communication system.Therefore,researches on photodetector with fast-response,high-power and high linearity is of great significance to the development of optical communication system.Partially depleted absorber photodetector(PDA-PD)with high-power and high linearity is widely studied by some scholars.The mushroom structure photodetector could improve performance of high-speed of photodetector.Novel mushroom PDA-PD with graded doping and mushroom dual-absorption layer PDA-PD were theoretically analyzed by combining the characteristics of mushroom structure and PDA-PD.The mushroom PDA-PD with graded doping was fabricated and tested.The main research work and achievements are listed as follow:1.Basic principles and common performance parameters of vertical illuminated partially depleted absorber photodetector were analyzed.And microcosmic characters of PDA-PD were studied in detail,such as electric potential,electric field distribution,carrier velocity,bandgap energy and carrier mobility.Meanwhile,the primary method of optimizing the quantum efficiency and high-speed performance of PDA-PD is proposed.2.2.5D(Cylindrical coordinates)simulation model of photodetector was built,along with the analyzation of P-doped absorption layer with graded doping profile and its affection on high-speed characteristic.By the comparison analysis,the 3dB bandwidth and efficiency bandwidth product(BEP)achieved their maximum value at a 6?m active area diameter,a 20?m barrier area diameter and an 890nm absorption layer thickness.After optimization,the mushroom structure PDA-PD with graded doping achieved a 3dB bandwidth of 28.2GHz,a quantum efficiency of 42%.Moreover,the quantum efficiency achieved 58%after integrating high-reflectivity grating.3.The mushroom dual absorption layer partially depleted absorber photodetector was designed and optimized,and the quantum efficiency improvement over traditional PD was studied and proved.In addition,the capacitance characteristic is thoroughly studied.In theoretical researches,the RC time constant of mushroom dual absorption layer PDA-PD has decreased 10%comparing to traditional dual absorption PDA-PD.Theoretical studies show that the QE of this novel structure was improved without sacrificing 3dB bandwidth.The optimized mushroom dual absorption PDA-PD achieved 52%of quantum efficiency and 37.2GHz of 3dB bandwidth.4.Etching process of InP-based epitaxial wafer and fabrication of mushroom structure were accomplished.A two-step photoetching method in fabricating mushroom absorption layer structure was proposed.The phenomenon of selective corrosion on different crystallographic orientations is analyzed.The mushroom structure is observed by using scanning electron microscope(SEM).5.The fabrication and test of a mushroom PDA-PD with graded doping were accomplished.The testing program includes dark current,external quantum efficiency and 3dB bandwidth.The 3dB frequency response bandwidth at-5V bias voltage is 5.2GHz,The dark current of the photodetector is 1.75×10-8A at a reverse bias of-5V.The 3dB bandwidth and external quantum efficiency are 5.2GHz and 26.92%at 1550nm,relatively.