Research Of High Speed And High Saturation Photodetectors For RoF System

In the wave of information technology, global communication traffic is experiencing explosive growth, and existing network bandwidth can not meet people’s needs. Rely on its abundant spectral resources, millimeter-wave wireless communication can provide high-capacity communication bandwidth for high-speed data. But millimeter-wave attenuates severely in the atmosphere and its transmission distance is limited. As optical fiber communication adopts photon as carriers, long transmission distance can be achieved. However, its mobility is poor and can not provide flexible access service. By combining the advantages of both technologies above, RoF system can achieve long-distance cable transmission and large-bandwidth wireless access, which has a very broad application prospect.In RoF system, the optimization of device is the key to improve the system performance. At optical receiver, higher response rate and greater output power photodetectors are needed. High-speed photodetectors can respond to high-bit-rate optical signals quickly, and high-saturation photodetectors can be able to withstand high-power optical injection and output large photocurrent. Therefore, high speed and high saturation photodetector has become a research focus of this thesis.The main research work and achievements are listed as follow:1. Basic principles of PIN-PD and UTC-PD are comparatively studied. In UTC-PD, holes can respond qucikly in dielectric relaxation time, and transit time is only decided by electrons. Compared to PIN-PD, UTC-PD eliminates the effect of low-velocity holes on bandwidth and has more excellent high speed high saturation performances.2. The2D simulation model of photodetector is established. The microcosmic characteristics such as energy band, electric field and carrier mobility in UTC-PD are analyzed in detail. The relations between UTC-PD performances and each layer’s thickness and doping are studied in-depth. According to theoretical research, enhancing the electric field intensity in the absorption layer is an effiective method to improve high speed and high saturation performances of UTC-PD, which can accelerate transport velocity of electrons and reduce the space charge effect.3. The optimization design for high speed and high saturation UTC-PD is investigated. The influences of adopting Gaussian doping and incorporating cliff layer on the performances of UTC-PD are discussed. By simulation, it is found that high speed and high saturation characteristics of UTC-PD are significantly improved. Finally, a3dB bandwidth of58GHz, a responsivity of0.28A/W and a saturation current of158mA are achieved.4. Zero-bias performances of PIN-PD and UTC-PD are theoretically studied. At zero-bias, simulation results show that electric field intensity in depleted region of PIN-PD and UTC-PD are1.28×104V/cm and2.8×104V/cm, and3dB bandwidth of PIN-PD and UTC-PD are7.5GHz and25GHz. Compared to zero-bias PIN-PD, zero-bias UTC-PD has obvious advantage in high speed performance and is expected to be applied into the high-speed and low-power-consumption optical communication systems in the future.5. The quality testing and fabrication of UTC-PD are accomplished. The performances of UTC-PD are tested. For the optimized UTC-PD at3V bias and1550nm wavelength, dark current is7.36X10-9A, quantum efficiency is23.57%and3dB bandwidth is7.02GHz.