| Modern technologies are emerging,such as Internet plus initiative,data centers,artificial intelligence and smart cities and so on.As the modern information society is about to enter the 5G,the amount of data continues to rise promptly.It is expected that the global network traffic will continue to grow at an exponential rate of about 45%in the future.However,due to the inherent scale difference between Moore's law of digital integrated circuits and high-speed analog optoelectronic technology,the interface rate and optical fiber capacity only increase by about 20%per year,resulting in the phenomenon of "constant shortage"of network bandwidth capacity.Therefore,the research direction of"constant invariability" is to improve system speed.The photodetector is the core component of the optical communication system.Its performance directly affects the performance of the whole system.In ultra-high speed,ultra-long-distance optical fiber communication system and data center communication,the optical detector needs to have high speed and high quantum efficiency at the same time.In order to improve the high speed and high quantum efficiency performance of the photodetector in the optical communication system,theoretical and experimental research on the high performance photodetector based on optical field manipulation and the microstructure is carried out.The main innovation points and research results of this dissertation are as follows:1.By the theoretical analysis,it is found that improving the carrier distribution in PIN-PD can improve the performance.In order to improve the performance of the photodetector,a new idea is proposed that the internal carrier distribution can be improved by changing the incident light field distribution.Three kinds of beam waist size Gaussian distribution light and the uniform distribution light were used for top incidence of the ring shape P-electrode PIN photodetector with mesa.Under-3V bias voltage,the bandwidth of the PIN-PD with a diameter of 10 ?m and absorption thickness of 400nm reaches 62GHz under the uniform light,which is about 63.2%higher than that of 38GHz with Gaussian distribution with the smallest beam waist.At the same time,the total power of uniform incident light with the same peak value is greater than that of several Gaussian distributed light,and the quantum efficiency is the highest.The quantum efficiency of incident light with the same peak is 35%.2.It is found that the carriers generated by uniform light in the absorption layer are distributed evenly in the horizontal direction,and the electric field is also uniform.The Gaussian distribution light makes the concentration of the carrier near the axis be higher,the electric field collapse at the symmetry axis of the device,and the capacitance increase.Therefore,uniformly distributed light produces a higher 3dB bandwidth than the Gaussian light.3.When three kinds of Gaussian distributed light with different beam waist size and uniformly distributed light incident to the photodetector with the same power,the uniform light incident PIN-PD obtained a higher frequency response than the other three.Under-3V bias voltage,the bandwidth of PIN-PD with diameter of 10?m is 56GHz at the uniform light incident with optical power 1.5mW.Compared with the minimum beam waist Gaussian distribution,the bandwidth of the uniform light increases by 47.37%.At the same time,the output current of the uniform incident light with the same power is the highest,and the responsivity is also the highest.When the incident light is uniform,the device's responsivity is 0.315A/W,which is 166.95%higher than that of the Gaussian light with the smallest beam waist,indicating that the output current is reduced due to the concentration of the photogenerated carriers at the device axis due to the Gaussian light.4.A "horizontal optimization" method is proposed to improve the performance of the photodetectors by adjusting the distribution of the incident light field on the photosensitive surface of the devices.The incident light field with annular distribution is designed accordingly.When the narrowest ring light incidents on the surface of the PIN-PD with the diameter of 10?m and the offset of its peak light intensity and the central axis of the device is 4?m,the maximum bandwidth is 68.31 GHz,which is about 20%higher than the bandwidth of the uniform light.5.The light field manipulation element is proposed to control the incident light field of the photodetector.The grating is used to reshape the incident Gaussian distribution light into the uniformly distributed light or the annular distributed light,respectively.Based on the grating with large period,a flat-top distributed light field is designed,and the Gaussian light of 1550nm incident light was transformed into the uniformly distributed light.When the grating period and duty cycle were 8.4?m and 0.5,the spot diameter of the output light was 5.1?m,and the transmittance is about 86%.A circular light field is designed based on a concentric ring InP subwavelength grating with the high refractive index difference with convergent function.The transmittance and deflection angle of TM light or circularly polarized light with the wavelength of 1550?m were 90.28%and 44.8°,respectively.6.A Hole-Groove Microstructure PIN Photodetector(HG-MPIN-PD)with the "center hole+surrounding Groove" is proposed,designed and fabricated.The optical path is changed by using the reverse cone and the V-groove microstructure.Increase the travelling time and the optical path of the light transmission in the absorber layer,forming the "light trapping" effect,and maintain or even improve the absorption of the light while reducing the capacitance of the device,so that the bandwidth and the quantum efficiency of the photodetector are improved simultaneously.The bandwidth of the HG-MPIN-PD with a diameter of 36?m,absorption layer thickness of 1.3?m,hole depth of 1.9?m,the diameter of the central hole and V-shaped groove is 10?m,and the hole-groove distance of 2?m reaches 21.72GHz under-5V bias voltage,and the quantum efficiency is 61%.When the hole-groove distance is 5?m,the bandwidth-efficiency product is 84%higher than that of the flat-top photodetector with the same structure.According to the shape of the P contact of the HG-MPIN-PD,a "steering wheel" shape P electrode is designed,and the S21 parameters of the electrode are simulated.The bandwidth of the electrode is greater than 100GHz,which fully meets the optical bandwidth requirements of the designed HG-MPIN-PD.7.The Al2O3 limiting layer with a certain radial length is fabricated around the P doping layer and the N doping layer of the HG-MPIN-PD and the absorber layer in the middle is used to form the leak-proof waveguide structure.The SiO2 antireflection film at the inclined side of the microstructure is designed to further enhance the light absorption.The quantum efficiency of the HG-MPIN-PD with the diameter of 8?m,absorption layer thickness of the 600nm,Al2O3 limiting layer and antireflection film is up to 42.9%,which is 127.8%higher than that of the ordinary flat-top PIN-PD.8.A kind of GaAs HG-PIN-PD with working wavelength of 850nm,a diameter of 44?m and a central hole diameter of 8?m is obtained.The dark current is about 0.02nA when the spacing between holes and V-groove changes from small to large,and the bandwidth is 14.34GHz when the spacing between holes and groove is 5?m.The highest bandwidth-efficiency product is 13.5GHz when the hole-groove distance is 7?m and the incident light power is-0.12dBm.A kind of InGaAs material,HG-PIN-PD with working wavelength of 1550nm,diameter of 44?m,center hole diameter of 8?m,hole-groove distance of 5?m,is prepared.Under-3V bias voltage,the measured photocurrent is 0.379mA,and the bandwidth is about 1GHz.The test results are lower than the results of the simulation optimization.This may be caused by the poor insulation of the device substrate.9.Two kinds of light with different beam waist sizes are used to incident on the GaAs PIN-PD with a diameter of 70?m.When the incident power is the same,the bandwidths of the two lights with different uniformitiy are about 13GHz and 11 GHz,with a difference of about 2GHz,which preliminarily verifies the conclusion that the bandwidth of the uniform distribution is higher.10.For the research of the mixer in the front end of the balanced photodetector in the coherent receiver,a phase delay power splitter is designed based on the one-dimensional SOI sub-wavelength gratings with converging function.When the TM polarized light with wavelength of 1550nm is incident at an angle of 45 degrees,the ratio of transmitted light power is very close to 1:1,and the transmittance is about 97.44%with phase delay of ?. |
PDF Full Text Request