| Infrared has the characteristics of strong penetration ability and strong thermal effect,which makes infrared photodetectors（PDs）widely used in military,medical,industrial,and other fields.Although traditional In Ga As and Hg Cd Te infrared PDs have excellent performance,their complex manufacturing processes,high costs,and the need for refrigeration technology make them difficult to widely use in the civilian field.Infrared PDs based on quantum dots（QD）have advantages such as solution process,low cost,adjustable wavelength and high absorption coefficient.Lead sulfide（PbS）and lead selenide（PbSe）QDs can cover the entire short-wave infrared（SWIR）band by adjusting their size due to the quantum confinement effect.Therefore,PbS（e）QDs have become a popular research target for SWIR PDs.PbS（e）QDs have relatively excellent photoelectric performance,but they possess many surface defects.Therefore,suitable ligands are needed to passivate QD to reduce surface defects.Most researchers focus on the passivation of small-sized QDs and have achieved promising results.However,as the QD size increases,the（100）crystal face of the QDs is gradually exposed,leading to irreversible oxidation and aggregation of the QDs.Accordingly,it is urgently required to develop new passivation methods for large-sized QDs.In this paper,key parameters affecting detector performance were investigated by SCAPS simulation,and selecting the PbS QDs with a more mature synthetic scheme as the research object.A mixed I-/Br-ion passivation method was proposed to passivate the 1300nm QDs.In this way,we try to reduce the defect density and increase the carrier mobility and further realize the imaging application based on the improved performance device.The main research results are as follows:（1）The performance simulation of PbS（e）QD PDs using SCAPS shows that low QD mobility and high defect state density are the main factors of limiting the performance.In addition,the thickness of the functional layer,doping concentration,and band alignment also has a certain impact on device performance.In addition,simulation results show that the performance of PbS QD PDs is better than that of PbSe QD PDs.（2）To reduce the density of defect states on the QD surface and improve the carrier mobility,this paper innovatively proposes a mixed I-/Br-ion passivation method and compares it with the single-ligand passivation of I-ions.The mixed halogen ions can effectively passivate large-size PbS QDs,as evidenced by the 80%increase in ligand coverage,the reduction of surface defects to 5.26×1015cm-3,the increase in mobility to 9.4×10-3cm2V-1s-1,and the stronger coupling between QDs by the mixed ion passivation.（3）Infrared PDs were fabricated using two different ligand-exchanged QDs and tested for their performance.It was found that halogen ion mixed passivation can effectively reduce QD surface defects,resulting in greatly improved carrier defect recombination,increased charge recombination lifetime,faster transfer of photogenerated electrons at the interface,easier charge extraction,and higher implantation efficiency.The PDs based on QDs with mixed passivation of halogen ions has a response of 0.557 A/W and a specific detection rate of 2.70×1013Jones,response time as short as 1.48μs.Compared to detectors with single I-ion passivation,their performance has been improved.（4）To verify the imaging capability of the QD PD,point element scanning imaging was performed using a halogen ion hybrid passivated detector.The“NCU”letter image with a resolution of up to 14400 pixels was obtained with smooth pattern edges and a good imaging effect.The result confirms the imaging capability of the PD prepared in this paper,and is expected to further realize the surface array imaging. |
