In resent days,the research team led by Prof.Ni Zhenhua and Prof.Wang Jinlan from the School of Physics,188滚球投注 utilized the defect engineering to upgrade the properties of two-dimensional photoconductor.Their research achievement titled "Defect Engineering for Modulating the Trap States in Two-dimensional Photoconductor" has been published on important periodical in the field of material: Advanced Materials.
Thephotoconductor,as a kind of device that transfers light toelectrical signal,has been deemed as one of the key technologies that can exert effect on our daily life,science & technology,and national defence,etc.such as video imaging,photo-communication,biomedical imaging,sensing,night viewing,securityandmilitary reconnaissance,etc..Since the defect state of the semiconductor material,as the trapping centre,can prolong the life of carriers effectively,the introduction of photoconductiongains can increase the sensitivity of photoconductorto a large extent;however,the trapping centre,especiallywiththeintroduction of deep trap,can increase the device'sresponsetime sharply mainly because it takes additional time for thecarriers to get rid of the trap of defect state.Moreover,such time also depends on the level of defect state (Fig.1).It has been always the difficulty confronted in this field to achieve rapid response while the device's high sensitivity can be guaranteed as well by means ofthecontrol of defect state andtrapping centre.Incontrast totraditional semiconductor materials,the energy band structure of two-dimensional materials can modulatein a more effective way though the surface and defect engineering;besides,it has also provided idealresearchobject to find solution to the said difficulty.
Schematic diagramofthe process of stimulation,recombination and trapping of photon-generated carriers in n-type semiconductor (including the trap state atdeepand shallow energy levels) (a),and the response time of corresponding device engaged in these processes (b)
The two-dimensional materials include diversified defects andcanexert significant influences on their electrical,optical,magnetic and mechanicalproperties,etc..In early 2018,Prof.Ni Zhenhua cooperated with the research team led by Prof.Chen Wei.They published an overview paper titled "Two-dimensional transition metal dichalcogenides: interface and defect engineering" on Chemical Society Reviews,which analysedthe impact of defect andinterface states on the electrical and photoelectric properties of two-dimensional chalcogenides in detailand how tomodulatethe properties of two-dimensional electronic/photo-electronic devicesbymeans of the defect and interface engineering.
In this work,the researchteam led byProf.Ni Zhenhua and Prof.Wang Jinlan,taking ReS2as a study case,initiated from the experiment andcomputational simulationrespectively,then proposed utilizingthe defect engineering to control the trap state of carriers in the two-dimensional photoconductor.The researchresult indicated that theoxygen atom in the protoporphyrin (H2PP) molecule can bind to the surrounding rhenium atom at the sulphur vacancy of ReS2and function in regulating the band structure and the defect energy levels.Compared with the photoelectric response dominated by the deep trap in the original sample,the photo-response of the modified device would be dominated by the shallow trap and the recombination centre,meanwhile,the response speed has been increased bythreeto four orders (Fig.2).In addition,since there'sa strong charge transfer between H2PP molecules and ReS2,the surplus electrons in ReS2can be extracted,thereby greatly reducing the dark current and noise of the device while enabling the light detection rate of the modified device to reach 1.89x10^13 Jones.This work has provided a research idea about how to control the trap state of photo-induced carriers in semiconductors through the defect engineering,which would be conducive to achieve two key indicators of high sensitivity and fast response in photo-detectors simultaneously.
Response time curve of ReS2photo-detector before/after H2PP molecular modification
The first authors of this paper are Dr.Jiang Jie and Dr.Ling Chongyi from the School of Physics,188滚球投注;Prof.Ni Zhenhua and Prof.Wang Jinlan are the joint corresponding authors.Thisproject has been sponsored by National Key R&D Program andNatural Science Foundation of China (NSFC),etc..
Advanced MaterialsDOI:10.1002/adma.201804332 (2018): https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201804332
Chemical Society Reviews 47,3100 (2018): http://pubs.rsc.org/en/Content/ArticleLanding/2018/CS/C8CS00024G#!divAbstract