Performance Optimization On Vertical Illuminated Pin Photo-Detector For Optical Communication

In the21st century, with human society entering the fast-growing information age, the global data services are experiencing explosive growth while the requirement for high network bandwidth is becoming imperative. To address this issue, the demand for optical fiber communication system with ultra-large transmission capacity, ultra-long transmission distance and ultra-high transmission rate becomes more urgent. PIN photodetector for optical communication is one of the key devices in the optical fiber communication systems. In order to optimize its performance so as to meeting the requirement for optical communication systems, this thesis mainly investigates the optimization methods for both InP-based PIN photodetector and dual-absorbing layer PIN photodetector. The fabrication and test of an InP-based graded doping PIN photodetector is accomplished.The main research work and achievements are listed as follow:1. Basic principles and common performance parameters are analyzed for vertical-illuminated PIN photodetector. Simulation model for high-speed PIN photodetector is established, through which the microcosmic character such as electric field distribution, bandgap, refractive index and carrier mobility of the photodetector are studied in detail. Then the primary method to optimize the high-speed permformance and quantum efficiency of PIN photodetector is proposed.2. The performance optimization design for vertical-illuminated PIN photodetector used in optical communication is investigated in depth, and the influence of gradient doping concentration and the gradient band gap is discussed. The simulation results illustrate a detailed comparison of the frequency response and quantum efficiency for photodetector with and without optimization. For a certain junction area (200μm2), the maximal bandwidth-efficiency product can be obtained with an absorption layer thickness of350nm. After optimization, the3dB bandwidth of PIN photodetector improves from20GHz to70GHz at1550nm with the external quantum efficiency increases to25%.3. A novel dual-absorbing layer PININ photodetector structure is proposed, which can implement a superior performance than traditional PIN photodetector and dual-absorbing layer PINIP photodetector with respect to both quantum efficiency and high-speed character. Meanwhile, this photodetector structure owns the advantage of simple fabrication process, mature technology and a wide range of application. After optimization, the3dB bandwidth of PININ photodetector is improved from40GHz to100GHz while the external quantum efficiency is boosted from23%to36%at1550nm.4. The epitaxial wafer growth and quality test of an InP-based graded doping PIN photodetector is accomplished. The actual structure of epitaxial wafer and doping concentration of each layer are obtained by quality test. The simulation results of epitaxial wafer indicate an external quantum efficiency of25%and a3-dB bandwidth of18GHz. The reason of the degradation of high-speed performance is also analysed.5. The fabrication and test of an InP-based graded doping PIN photodetector is accomplished. The test data include dark current, external quantum efficiency and3-dB bandwidth. The3-dB frequency response bandwidth at zero bias voltage is12.4GHz, which is numerically above eighty percent of that at reverse bias of3.3V, which is15.09GHz. The dark current of the photodetector is9×10-8A at a reverse bias of0.1V, while the external quantum efficiency of the single photodetector is21.14%at1550nm, which means the responsivity is0.26A/W at1550nm. The experimental results are consistent with estimation and simulation. Upon all these data, this zero bias voltage photodetector will be expected to apply in low power-loss photo-communication sensor system in the future.