Research Of Black Si Material Fabricated By Pulsed Laser Irradiation And Its Applications In Infrared Optoelectronic Detections

Silicon-based photonic devices have attracted extensive attention worldwide because of their low cost and good compatibility with integrated circuit technique.In the past twenty years,silicon photonics is in a stage of vigorous development,and more and more silicon-based photonic devices have been used in the field of optical communication and optical interconnection.Up to now,among all the silicon-based photonics devices,COMS compatible low loss waveguide,high Q resonator,high speed modulator,and optical pump laser have been achieved.All of these devices can be used in the optical communication waveband,such as 1310 nm and 1550 nm.However,fabrication of silicon-based photodetectors is still an obstacle which hiders the development of silicon photonics.Development of silicon-based bulk structure photodetectors has a long history.However,the response wavebands of commercial silicon photodetectors are below1100 nm due to the 1.12 eV energy gap of crystalline silicon.Employing super-saturated black silicon material turns out to be a solution.Surface micro-structured black silicon material can be achieved after femtosecond laser irradiation in SF₆ atmosphere.The black silicon samples exhibit near-unit high absorptance of more than 90%during a long waveband from 0.25?m to 6.0?m.Soon after,black silicon fabricated by pulsed laser irradiation was used in making silicon based infrared photodetectors and a bulk structure silicon photodiode with a responsivity of 50 mA/W for 1310 nm light has been achieved.Despite its huge potential,research of laser-irradiated black silicon shows little progress in the past 20years due to the complexity of the physic and chemical states in the laser irradiated layer.So,gaining insight into the optical and electrical property of the black silicon material turns is very essential.In the paper,black silicon samples with high infrared absorption has been made by pulsed laser irradiation.Then the material property was characterized from the following aspects:research of absorption mechanism,Optimization of optical properties,photodiode fabrication.The ultimate goal is to obtain a proper material for silicon-based infrared light fabrication.In details:?1?Absorption mechanism of laser-irradiated black silicon is explored to make clear the contribution of defect states in the infrared absorption of black silicon material.The depth profile of infrared absorption-related defect states in the silicon surface layer is measured through a surface etching experiment.Absorption contribution of both the surface re-solidified layer and the pressure induced phase-transformation layer is verified.?2?Phosphorus doped black silicon material with thermal stable infrared absorption is fabricated by fs laser irradiation.An environmental friendly solid-state phosphorus diffusion method is proposed.Through phosphorus doping,impurity diffusion induced absorption reduction during thermal annealing process has been solved and black silicon material with thermal stable absorption has been achieved.Three different absorption mechanisms are proposed and analyzed in detail through absorption efficiency calculation.?3?Nitrogen doped black silicon material with low free carrier concentration has been fabricated by fs laser irradiation in nitrogen atmosphere.Absorption contribution of nitrogen doped into amorphous silicon phase has been verified by first principles calculations.Photodiodes which can operated at 1310 nm are made with nitrogen-doped black silicon.The responsivity of the photodiode is enhanced by inducing infrared absorption layer on both side of the photodiode.?4?Properties of black silicon samples fabricated with nanosecond laser irradiation on high-resistivity silicon substrate are explored.A defect-states induced resistivity reduction phenomenon is observed on the silicon surface layer after ns laser irradiation.The resistance reduction phenomenon is independent of ambient gas during laser irradiation and the conduction type of silicon substrate.Photodiode with high responsivity at 1310 nm is made with non-doped black silicon substrate fabricated by ns laser irradiation in argon.?5?Optical and electrical property of impurity supersaturated silicon material fabricate by ion implantation are explored.Fs laser annealing method is proposed to repair the ion implantation induced defects as while as inducing microstructures on silicon surface layer.Photodiode which can operated at 1310 nm are made with pulsed laser annealed materials.In summary,this paper aims at making silicon-based infrared photodetectors oprate at optical-communication wavebands.To achieve this goal,attempts are tried by adjusting material property and optimizing device structure.Pulsed laser irradiation is used for making black silicon substrate with high infrared absorption.Properties of black silicon samples can be controaled through choosing proper doping impurities and optimizing laser parameters.Investigations of black-silicon materials and photodiodes in this paper accelerate the development of silicon-based photodetection domain.