The Study Of Wide-spectrum And High-speed Photodetectors Based On Photonic Crystals

The rapid development of the Internet,cloud computing,and the Internet of Things has created a huge demand for the development of high-speed,large-capacity information transmission technologies.Optical fiber communication systems need to be continuously developed to meet the capacity requirements of the ever-increasing data transmission volume.Traditional single-mode fiber(SMF)is approaching its theoretical capacity limit.Broadening the existing communication frequency band is considered to be a promising solution to the problem of capacity shrinkage.The widening of the communication frequency band puts forward higher requirements for the performance of the optical receiving end.As an important component of the optical receiving end,it is of practical significance to study high-speed photodetectors with high response in a wide spectral range.The researchers found that the targeted design of photonic crystals can effectively control the behavior of light,and fabrication of photonic crystals in devices has become one of the common strategies to improve the performance of optoelectronic devices.In this thesis,a wide-spectrum,high-response,high-speed photodetector for near-infrared optical communication needs is investigated by utilizing the light-harvesting properties of photonic crystals.A vertical photodetector with a two-dimensional photonic crystal structure is designed and fabricated,and an in-depth research is carried out on the impact of the introduction of photonic crystals on the important performance of the photodetector.The specific work is as follows:In the vertical p-i-n photodetector structure,a thin absorption layer is used to achieve high-speed performance.At the same time,a vertical two-dimensional photonic crystal is designed on the surface of the detector,and the light trapping property of the photonic crystal is used to confine the vertically incident light to the detection area and fully absorb it,so as to improve the responsivity.In this thesis,the optical design is firstly carried out,and the period,hole radius,etching depth and other parameters of the photonic crystal are optimized by the FDTD Solution simulation software.A photonic crystal structure with a period of 1080nm,a hole radius of 400nm,and an etching depth of 280nm is designed on a Ge Sn photodetector.The simulation results show that the absorption efficiency of the device structure at the wavelengths of1550nm and 1650nm can reach 80%and 63%,respectively..After that,the process design and actual tape-out of the Ge Sn photonic crystal photodetector are carried out,and the volt-ampere characteristics,responsivity and 3d B bandwidth of the device are tested and analyzed.The data shows that the dark current of the device with a mesa diameter of 18μm is about 510n A under 1V reverse bias,corresponding to a dark current density of 0.20A/cm2,showing good voltammetric characteristics.The photonic crystal detector with an absorber layer thickness of only360nm has high responsivity of 0.50A/W and 0.13A/W at 1550nm and 1650nm,respectively.After that,the process design and actual tape-out of the Ge Sn photonic crystal photodetector were carried out,and the I-V characteristics,responsivity and 3d B bandwidth of the device are tested and analyzed.The data show that the device with a mesa diameter of 18μm exhibits a dark current of 510n A and a dark current density of0.20A/cm~2,which are lower than expected values.The responsivity of the device with an intrinsic absorption layer thickness of only 360nm is at 1550nm and 1630 nm,respectively.The 0.50A/W and 0.13A/W,18μm mesa diameter devices have a 3d B bandwidth of about 3.1GHz at 1550nm under 3V reverse bias.The 3d B bandwidth of a device with a mesa diameter of 18μm under 3V reverse bias is about 3.1GHz.Finally,on the basis of the performance test of Ge Sn photonic crystal detector,compared with the detector without photonic crystal,the influence of the introduction of photonic crystal on the important performance of the detector is discussed.The absorption spectrum,dark current,responsivity,frequency response,etc.of the two devices are compared and analyzed.The introduction of the photonic crystal structure broadens the absorption spectrum of the detector and increases the responsivity of the detector at 1550nm and 1650nm wavelengths by 2.4 and 3.9 times,respectively.At the same time,the dark current of the device is reduced by an average of 33%,and the 3d B bandwidth at 1550nm is increased by 2.6 times.