Research On Photodetectors With High Responsivity For Underwater Visible Light Communication

With the increasing emphasis on the development of marine resources in the world,and the detection activities related to the oceans are becoming more frequent.Compared with other traditional underwater acoustic communication technology,underwater visible light communication(VLC)is a wireless communication method with high speed,large capacity and strong confidentiality.Therefore,it has become one of the most important technologies.Scattering occurs when light travels through the water,causing the beam energy to decrease as the transmission distance increases.How to design photodetectors with high responsivity for weak light environments and improve the transmission distance of underwater visible light communication have become an urgent problem.According to the requirements of underwater VLC for photodetectors,this thesis studies the photodetectors with high responsivity based on CMOS technology.The main contents include:1.Based on the subthreshold amplification effect of MOS transistors,a gate body tied NMOS photodetector with high responsivity was designed.where the T-well and the deep N-well provided by the UMC 0.18?m CMOS process form a photodiode,and the photo-generated current generated after the light-sensing is amplified by the NMOS transistor,thereby effectively improving the responsivity of the photodetector.Simulation and test results shown that the NMOS photodetector has high responsivity in the visible wavelength range.In order to solve the problem of low bandwidth of the NMOS photodetector,the T-well regions are divided into 2×2 and 4×4 structures,which effectively reduces the transit time of the photo-generated carriers in the T-well.The bandwidths are increased to 850MHz and 2GHz respectively.2.Based on the CSMC 0.25?m CMOS process,a high responsivity single photon avalanche diode(SPAD)photodetector using the avalanche multiplication effect was designed.The N buried layer is used to form a virtual guard ring,a SPAD with a double guard ring structure was formed by combining with the P-well guard ring,which effectively suppresses edge breakdown of the device.The simulation results shown that the SPAD has higher responsivity and photon detection efficiency.3.A double gate tunneling field effect transistor(TFET)detector with high responsivity was designed by combining the photodiode with the TFET based on SOI technology.The photogenerated potential of the photodiode is used to regulate the channel barrier of the TFET,thereby controlling the TFET output current,and realizing the conversion of the light signal to the current signal.The simulation results shown that the TFET detector has high responsivity to weak light detection.When the light intensity is less than 10m W/cm~2,the responsivity of TFET photodetector can exceed 10~4A/W.The photodetectors designed in this thesis meet the requirements of the underwater VLC system,and the results provide a reference for the design of underwater VLC.