The Study Of 1550nm High-speed PIN Photodetectors

Since the human society entered the information age marked with internet and multimedia,the rapid development of video,multimedia,streaming media,mesh grid computing,file backup,etc.demands higher transmission speed and capacity.Nowadays,optical fiber achieves high bandwidth about 30 THz,low transmission losses,strong anti-electromagnetic interference capability,and low cost,which makes fiber a key medium for data exchange.And fiber communication therefore comes out to be the pillar of transmission technology.Among the fiber transmission windows,1550nm has lowest loss,and is most widely used in communication systems.In this paper,for the application of high-speed fiber communication system at 1550nm,the influence of the material and structure on devices performances is studied,and a high-bandwidth detector is fabricated.The research results of this paper are shown as following:1.The Ge/Si high-speed detector was designed and fabricated.The diameter of mesas of the device are 15?m,20?m,25?m,40?m,80?m and 100?m,respectively.The dark current density is 25.5mA/cm²,the coefficient related to surface area is21.73mA/cm²,and the coefficient associated with the circumference is only 8.23?A/cm,which means that the dark current of the device is mainly derived from the bulk structure.In addition,the device's responsivity is 0.249A/W@1550nm,and the 20?m diameter device bandwidth is 20.9GHz@-0.5V.2.Dark current of the device is measured at a temperature range from 100K to280K.When the operating temperature of the device is higher than 240K,ideality factor is approximately 1 and the numerical fitting indicates that the value is fitted well with the Shockley-Read-Hall recombination current.At this situation,the dark current of the device is dominated by diffusion current and the SRH recombination current.When the temperature is lower than 220 K,the dark current is determined by the trap-assisted-tunneling enhanced recombination current.The activation energy is extracted as Ea?0.16eV,which is lower than₂¹E_g-Ge.Trap-assisted-tunneling is therefore the main mechanism that effects the dark current.By comparing the responsivities at 850nm,1310nm and 1550nm,it's found that the absorption coefficient of strained germanium impacted by SiGe interface is much lower.At high operating frequency,interface states barely affects the bandwidth performance of the devices.3.InGaAs/InP high-speed detectors was designed and fabricated.Utilizing the equivalent circuit and the carriers transition model,when the diameter is 75?m,the thickness of device intrinsic layer equals to 2.1?m,where the 3dB bandwidth reaches peaking.Based on transfer matrix method,the maximum absorption efficiency is obtained as 90.07%,when the thicknesses of oxide and top InP are 276nm and 100nm,respectively.Based on the band theory,in order to weaken the barrier at the heterojunction interface,the InGaAsP band transition layer is inserted,which increases the device 3dB bandwidth by 9.4%.After MOCVD epitaxy and micro-nano process,the detector is fabricated and the 3dB bandwidth achieves 4.93GHz,with responsivity of 0.676A/W at 1550nm,and dark current density of 58.97mA/cm².