| Shortwave infrared semiconductor photodetectors in the 1-3 μm wavelength are core devices in the fields of quantum communication,quantum computers,threedimensional sensing and 5G high-speed optical communication.They are widely used in military,commercial and civilian fields such as national defense,communication and autopilot.With the advancement of these applications,shortwave infrared semiconductor photodetectors are developing in the direction of high sensitivity,high speed and on-chip integration.To improve the performance of photodetectors,the development of new photodetection materials,the design of new device structures,and the on-chip integration of detectors are important research topics to promote the development of shortwave infrared photodetectors.In order to solve the problem about national selfdetermination of core photodetector chips,this thesis has made an intensive study on the key technologies,new materials and new structures of several typical photodetectors in the shortwave infrared band.The main research contents include:1.High sensitivity single-photon avalanche diode:Aiming at the design bottleneck of single-photon avalanche diodes in the epitaxial structure,the addition of an external optical structure is used to improve the device performance.The transmission matrix method is used to design the metal-distributed Bragg reflector to analyze the spectral reflectance efficiency of different incident angles,and to design an optimized Geiger mode avalanche diode by the wide-spectrum total reflector.Zn diffusion pretreatment,Zn diffusion characterization analysis and Zn diffusion cell structure are developed to optimize the process of fabrication.A complete fabrication process is developed,and a single-photon avalanche diode with an ultra-low intrinsic dark count rate(the active region diameter is 12 μm)is finally obtained.The self-optimized single-photon avalanche diode achieves high sensitivity and low noise characteristics,which has an ultra-low intrinsic dark count rate of 127 Hz at 10%detection efficiency,361 Hz at 20%detection efficiency,and 665 Hz at 30%detection efficiency(at the temperature of 233 K).And its intrinsic dark count rate is an order of magnitude lower than that of commercial devices under the same photon detection efficiency.Technical accumulation has been made to realize the localization of high-performance single-photon avalanche diodes.2.The exciton characteristics of the easy on-chip integrated few-layer black phosphorus:Aiming at the problem that the low absorption efficiency of the few-layer black phosphorus is difficult to be used as an optoelectronic device,a method of using metal nanostructures to generate coupling field enhancement is proposed to enhance the exciton resonance absorption peak of the few-layer black phosphorus.And use an anisotropic structure to improve the polarization sensitivity of the few layers of black phosphorus.Compared with the currently studied black phosphorus exciton resonance characteristics,the 4-layer black phosphorous exciton resonance peak is increased by 5.8 times,the absorption value is as high as 84%,and the polarization selection ratio is greater than 30.The application of the few-layer black phosphorus exciton effect based on coupling field enhancement in tunable,polarization-sensitive and on-chip integrated optoelectronic devices is prospected.3.High-speed uni-traveling-carrier photodiode enhanced by surface plasmons:To solve the design contradiction between the responsivity and the 3 dB bandwidth of the vertical uni-traveling-carrier photodiode,and the problem that the comprehensive performance of the current plasmonic photodetector is not as good as that of commercial devices due to the material quality,we proposed a plasmonic enhanced uni-travelingcarrier photodiode by combining metal nanostructure and uni-traveling-carrier photodiode.A high-performance photodetector with over 2-fold improvement in responsivity(improved from 0.052 A/W to 0.118 A/W)is realized,while its 3 dB bandwidth exceeds 40 GHz and its dark current is about 2 nA.And calculate the theoretical model(under the ideal condition:the thickness of the absorber layer is much smaller than the multiplication layer)of the best 3 dB and junction area to provide design ideas for 400 GHz photodiode.4.High-speed evanescently coupled waveguide photodetector:In response to the development needs of 100 Gbit/s and on-chip integration of optical communications,the evanescently coupled waveguide photodetector with an integrated tapered spot-size converter is studied.By optimizing the design of the vertically tapered spot-size converter and the geometric parameters of the epitaxial structure,the design of a 48 GHz evanescently coupled waveguide photodetector with high responsivity(0.63 A/W)and easy on-chip integration is realized.The main innovations of this thesis include:1.A broad-spectrum metal-distributed Bragg reflector is designed based on the transfer matrix method,and the reflector is used to improve the quantum efficiency of single-photon avalanche diodes with a small active area.A device with the excellent comprehensive performance of lower dark count rate and higher detection efficiency is obtained by the smaller area of the active region and the improvement of the quantum efficiency.A single-photon avalanche diode with an ultra-low intrinsic dark count rate in the active region with a diameter of 12 μm is fabricated,which is an order of magnitude lower than the intrinsic dark count rate of commercial devices under the same operating conditions of temperature and detection efficiency.2.The localized surface plasmon resonance generated by the anisotropic metal nanostructure is combined with the Fabry-Pérot resonance to realize the enhancement of the coupling field of the few-layer black phosphorus.The exciton resonance peak absorption value and polarization selectivity ratio of two-dimensional black phosphorus are enhanced by utilizing the near-field enhancement property of the coupling field enhancement generated by the metal nanostructure and the polarization selectivity property of the anisotropic structure.The designed structure increases the absorption at the resonance peak of the 4-layer black phosphorus exciton to 84%(5.8-fold)and maintains a polarization selectivity ratio greater than 30.3.We combine the localized surface plasmon resonance generated by the metal nanostructure with the uni-traveling-carrier photodiode.The sub-wavelength scale light trapping and field enhancement characteristics of localized surface plasmon resonance are used to improve the responsivity characteristics of the uni-traveling-carrier photodiode with a thin absorption layer.The added metal nanostructure makes the responsivity of the vertically incident uni-traveling-carrier photodiode with a 120 nm thick absorption layer doubled,without affecting the device characteristics such as dark current and 3 dB bandwidth.4.The photoelectric integration design method of the active and passive components of the evanescently coupled waveguide photodetector with an integrated tapered spot-size converter is proposed.By importing the optical field distribution of the absorption layer generated by optical simulation into the electrical simulation model as the photo-generated carrier distribution,the simultaneous simulation of the optical and electrical models is realized,and the closed-loop simulation of the optoelectronic performance of the waveguide optoelectronic device is completed.Based on this,a highspeed evanescently coupled waveguide photodetector with a 3 dB bandwidth of 48 GHz is designed. |
