Preparation And Properties Of High Performance Photodetectors Based On Two Dimensional Nano-materials

The technology of photodetection has been widely used in the fields of daily life,industrial manufacture,national defense,etc.Photodetector is regared as the most core component in the photodetecting systerm.With the development of photodetection for miniaturization,intelligent and low energy consumption,the conventional materials for photodetection have been suffering several disadvantages that are difficult to overcome.Especially,the demand for high performance infrared photodetectors in technology of national defense has been a long-term task.Therefore,looking for new materials is one effective method to realize broadband,high responsivity and ultrafast photodetectors.Recently,a new class of two-dimensional materials,such as graphene,transition metal dichalcogenides?TMDCs?,topological insulator?TI?and topological crystalline insulator?TCI?,has triggered extensive research because of their excellent properties,promising great opportunities for high performance photodetectors.However,there still be several critical problems in repsonse mechanism,device manipulation,comprehensive performance and mass production for the photodetectors based on the above mentioned materials.Based on the above mentioned problems,this thesis do researches on the four parts:electro-photo modulation of the fermi level in WSe₂/graphene heterojunction,the enhanced photoresponse of WSe₂/MoS₂heterostructure photodetector by PbS quantum dots,the broadband high responsivity photodetectors based on large-scale TCI SnTe and the broadband ultrafast photovoltaic detectors based on large-scale TI Sb₂Te₃/STO heterostructure.The main achievements are summarized as follows:1)WSe₂/graphene heterostructure has been fabricated by mechanical exfoliation and dry transfer method.The heterostructure exhibits high I_on/I_offratio?10³?in transfer characteristic in dark and distinct rectification behavior in output characteristic under light illumination,respectively.Time-dependent photoresponse reveals that the heterostructure has a considerable potential in the application of photodetection.Interestingly,an exotic current peak is observed in transfer characteristics under light illumination.This novel behavior is attributed to the tunable fermi level at the WSe₂/graphene heterojunction by electro-photo double modulation.The results may be helpful to develop tunable photovoltaic optoelectronics based on van der Waals heterostructures.2)To promote the absortion and photovoltaic response,WSe₂/MoSe₂ p-n heterostructure photovoltaic detector has been fabricated by mechanical exfoliation and dry transfer method.The prominent photoluminescence?PL?quenching effect in heterostructure area indicates effective charge transfer in hetero-interface,which will promote the charge separation and transportation.The WSe₂/MoSe₂ exhibits typical rectifying and photovoltaic behavior,suggesting a sharp,clean interface and large barrier height between WSe₂and MoSe₂.The photovoltaic response can be effectively controlled by back gate voltage.We study the mechanism for the short circuit current peak in transfer curve.By spin coating PbS quantum dots on WSe₂/MoSe₂ heterostructure,the responsivity has been improved by one order.3)A TCI SnTe photoconductive detector has been fabricated.The SnTe with high crystalline quality and large-scale?5 mm×2 mm?was grown by MBE method.A highly efficient photoconductive detector based on the as-prepared SnTe films features a fast and stable photoresponse from the visible to the mid-infrared range?405 nm-3.8?m? at room temperature.Moreover,the photodetector shows a high responsivity(3.75 AW^-1at 2003 nm).These results give a guideline for studying the intrinsic properties of TCIs and optimizing these devices for broadband and sensitive optoelectronic applications.4)Scalable,broadband photovoltaic detectors based on topological insulator Sb₂Te₃/STO heterostructure have been achieved.Large-scale?2 mm×5 mm?,high crystalline quality p-type Sb₂Te₃films were fabricated on n-type STO substrate by MBE method.The Sb₂Te₃/STO heterostructures exhibited pronounced photovoltaic behavior as a result of strong built-in field at the hetero-interface.Superior performances of broadband?from visible to infrared,405 nm-1550 nm?and ultrafast?rise time 30?s,fall time 95?s?photoresponse were achieved in ambient condition.The Sb₂Te₃/STO photodetector shows prominent photovoltaci effect in wide temperature range?100 K-500 K?and after the neutron irradiation.The prominent repeatability and stability indicated that our photodetectors can operate effectively in harsh circumstances.These results show that stacking the topological insulator thin films on strongly correlated oxide substrate using MBE approach holds great promise for high performance optoelectronic applications.