Characterization And Analysis Of Local Electric Field And Dark Current Mechanism Of New Concept Infrared Photodetectors

Infrared photon detection technology has been developed for nearly ninety years.At present,the development directions of infrared detection system are smaller size,lower weight,smaller power consumption,lower price and higher performance,which is often called SWAP3.In this context,the new generation of infrared detection technology will focus on preparation of high sensitivity and high operating temperature infrared photodetectors.And it has ushered in an era of rapid development.The synthetization and fabrication of mercury cadmium telluride has significant influence on infrared detection technology,for HgCdTe has extremely high photoelectric conversion efficiency,excellent carrier transport properties and advantages of the tunable response wavelength range along with the Cd component.Another more important thing is that HgCdTe owns large electron-hole ionization coefficient ratio in the mid and long-wavelength infrared range.For this reason it can be used as one of the most ideal materials for high-performance electron avalanche photodetectors.However,the researches on HgCdTe avalanche photodetectors in our country are still in its infancy:the material growth and device preparation technology are under development;the dark current and associated noise are very large;the avalanche ionization mechanism is still unclear;and the device evaluation has not yet formed one standard.Therefore,the research content of this topic is to study the influencing source of dark current and associated noise of HgCdTe avalanche photodetector,the optimal design of devices and the method of device evaluation by experimental measurements.In addition,for the future applications of SWAP3,the detection mechanism of novel two-dimensional materials and extrinsic silicon-based infrared photodetectors operating at room temperature is preliminarily discussed.The specific research contents and main research results of this topic are as follows:1.Researches on the dark current avalanche mechanism of planar and mesa avalanche photodetectors.Ion implantation and in situ doping are two important doping techniques for preparing plane and mesa HgCdTe electron avalanche photodetectors.Through the establishment of two-dimensional simulation model and compared with experimental results,the impact ionization phenomenon model was precisely proposed.The results show that different performances between planar and mesa HgCdTe avalanche photodetector should attributed to the doping and structure design of multiplication layer.The electric field intensity in the multiplication layer shows significantly effect on the generation rate of inter-band tunneling and impact ionization at-8 V bias.The results show that when the electric field intensity is 1.5 times larger,impact ionization rate could be more than 4 orders of magnitude different.In order to optimize the design of HgCdTe avalanche photodetector,it is necessary to avoid the local electric field.Only if the electric field is totally acting on the transport of photo generated carriers,the high performance and low noise devices could be obtained.2.Researches on the influence of non-uniform local field on avalanche photodetectors.Non-uniform local field is one of the main reasons affecting the performance of avalanche photodetector.We set up a laser beam induced current characterization platform,and measured the electric field of HgCdTe devices and In Ga As/In P avalanche photodetector with guard ring.The measured results show that 80?96 h annealing treatment can improve the carrier life in the etching area of HgCdTe material.It also shows that the guard ring can effectively suppress the transverse electric field introduced in the diffusion area and significantly inhibit the non-uniform peak electric field under the linear operation mode of In Ga As/In P avalanche photodetector.The characterization and suppression of non-uniform local fields can provide one effective way of reducing the dark current gain and preventing the pre-breakdown of avalanche photodetectors.3.Researches on the guard ring designs of mid-wavelength infrared avalanche photodetector.Ion-implanted HgCdTe avalanche photodetector has simpler process and shorter preparation cycle.In this work,one anneal-related graded junction model of mid-wavelength ion-implanted HgCdTe avalanche photodetector is proposed.The results show that the device bandwidth is mainly limited by carrier transport speed in the absorption layer,and the device bandwidth can theoretically reach 3 GHz.Additionally,we designed HgCdTe avalanche photodetector with shallow,medium and deep guard ring structure.The simulated results show that medium and deep guard ring can effectively reduce the dark current,reducing excess noise factor and improve gain to noise ratio.Compared with the device with no guard ring,dark current under the bias of-8 V decreased 1.6 times and 2 times,respectively.And gain to noise ratio is also nearly one order of magnitude higher than the device without guard ring.This work can provide basic theoretical guidance for the preparation of mid or even long-wavelength infrared HgCdTe avalanche photodetectors with the high signal-to-noise ratio.4.Study on the modeling and mechanism of high operating temperature two-dimensional material infrared photodetector.Based on basic analysis mechanism of the dark current and associated noise of traditional infrared detectors,the new concept two-dimensional material infrared detector is theoretically researched.In this work,absorption characteristics of two-dimensional materials were calculated.The results show that high-performance infrared photodetectors can be fabricated when the absorption coefficient of two-dimensional materials is larger than 10⁵ cm^-1.Taking BP with 100 nm thickness as an example,the calculated results show that the peak detectivity in mid-wavelength infrared range of BP devices could reach 6.3×10¹⁰ Jones.In addition,through TCAD modeling we obtained the advantages and disadvantages of mesa and plane two-dimensional materials devices with asymmetric characteristics.The reasons for two-dimensional materials devices with easy regulation and bipolarity characteristics were made clear,and at last some experimental observation phenomena was explained by proposed models.5.Preliminarily studies of high operating temperature extrinsic Si-based infrared photodetectors.Si chips represent the most mature semiconductor industry at present.However,limited by the intrinsic energy band of Si,it is not allowed to be used as an infrared?>1100 nm?photodetector.Therefore,Si based ultra-bandgap infrared detector based on the photoelectric effect is a significant work.In this work,the deep level defect band was introduced into Si,and then the limitation of Si intrinsic energy band was broken.Though the designed block impurity band structure,the extrinsic Si infrared detector with the ability of ultra-bandgap infrared detection was fabricated.The room temperature experiment results show that the 1000 K blackbody specific detectivity of fabricated device can achieve 4.5×10⁸ Jones with 1.1mm filter,the 1550 nm quantum efficiency can reach 6%,and the cutoff wavelength can reach mid-wavelength infrared.Furthermore,the microregion characterization of absorption spectrum,reflectance spectrum mapping and infrared imaging were obtained by the fabricated devices.