Design Of High-speed And High-power Uni-traveling-carrier Photodetector For Optical Communication

With the development of information society,the emerging business,represented by large data,cloud computing and networking have the demand for the bandwidth increasing rapidly.The existing optical communication systems are unable to meet the growing demand for interconnection capacity,so it is eager to enhance transmission capacity and bandwidth further.Faced with the requirements about network high speed and large capacity at present,developing ultra-high-speed,large transmission capacity and ultra-long optical fiber communication system has become the urgent problem.The photodetector as the key component of fiber optic communication system,plays an important role in the whole optical fiber communication system.High-speed and high-saturation photodetectors not only can respond to the high-bit-rate optical signals quickly,but also can obtain higher output saturation current.The main content of this work is to research and optimize uni-traveling-carrier photodetector(UTC-PD)for high-speed and high-power optical communication.Then the experiment fabrication and test of UTC-PD is accomplished.The main research work and achievements are listed as follow:1.Basic principles,performance parameters and small signal model of UTC-PD are analyzed.Then the 2D simulation model of UTC-PD is established.The carrier mobility,electric field distribution,refractive index and bandgap of the photodetector are studied in detail.At last the primary method to design the high-speed permformance,quantum efficiency and high saturation of UTC photodetector is proposed.2.The relationship between epitaxial layer structure parameters including thickness and doping and UTC-PD characteristics is analyzed.According to the research,improving the distribution of electric field in the absorbing layer and collecting layer can accelerate transport velocity of electrons and reduce the space charge effect,then the characteristic of UTC-PD bandwidth and saturation current can be improved effectively.While the phenomenon that the bandwidth of UTC-PD slowly increases at frist with the increase of incident light intensity,then decreases obviously is discovered and explained.3.An optimized structure of UTC-PD with high speed and high saturation is designed.The influences of adopting Gaussian doping and incorporating cliff layer on the performances of UTC-PD are discussed,and also studied the influence of the thickness and concentration of the absorption layer,cliff layer and the collecting layer on the performance of the device.The study shows that high speed and saturation characteristics of UTC-PD are improved obviously by using the optimized structure.Finally,the 3dB bandwidth of 53GHz,a responsivity of 0.33A/W and a saturation current of 120mA are achieved.4.To solve the problem that the traditional vertical incident detector is difficult to obtain both high bandwidth and high efficiency,a structure of UTC-PD with double absorption layer is proposed.Compared with UTC-PD with single absorption layer,the performance characteristics of double absorption layer structure are studied and analyzed.The research showed that under 2V bias and 1550nm wavelength,the responsivity of both were 0.33A/W and 0.17A/W,3dB bandwidth were up to 52.2GHz and 60GHz respectively.The bandwidth efficiency of the dual absorption UTC-PD has increased nearly 70%compared with the ordinary UTC-PD.Therefore,UTC-PD with double absorption layer structure can obtain high responsivity and quantum efficiency without sacrificing high-speed performance.5.The quality testing and fabrication of UTC-PD are accomplished.The dark current,quantum efficiency and 3dB bandwidth of UTC-PD are tested.Then the problems which appeard during the experiment are analyzed.For the UTC-PD at 3V bias and 1550nm wavelength,the experimental results show that dark current is 7.3nA,quantum efficiency and 3dB bandwidth are 28%and 11.2GHz respectively.