Constrction And Properties Of Vanadium Oxide Nanowires(Rods) Heterojunction Photodetectors

Hybrid dimensional van der Waals（vd W）heterojunction is one of the effective strategies to overcome the limitation of photoelectric properties of new nano materials.Most single nanostructure photodetectors only have light response performance in specific single wavelength light or narrow spectral range,while photodetectors based on novel vd W heterostructures can effectively improve the sensitivity of devices and expand the detection range.However,at present,the preparation method of one-dimensional/two-dimensional material vd W heterostructures usually adopts multi-step method,which is complex and expensive.Therefore,it is very challenging and valuable to develop a simple and inexpensive method to prepare hybrid dimensional vd W heterostructures.VO₂（B）and V₃O₇·H₂O nanowires（nanorods）have narrow band gaps and are expected to be used for broad spectral detection in the ultraviolet to near-infrared band.Two dimensional layered materials Mo S₂and Weyl semi metal T_d-Mo Te₂have a variety of unique properties.They can stack with other low dimensional materials to form vd W heterostructures,which can easily"cut"the advantages of these materials to further improve the photosensitivity.Taking these materials as research objects,this paper developed a simple and low-cost mechanical stacking method to prepare mixed dimension VO₂（B）nanorods/Mo S₂and V₃O₇·H₂O nanowires/T_d-Mo Te₂vd W heterostructures,and built photodetectors.It was compared with VO₂（B）nanorods and V₃O₇·H₂O nanowires photodetectors,and analyzed and discussed the physical mechanism of performance improvement.The main research contents are as follows:（1）Using V₂O₅as vanadium source and oxalate as reductant,a hydrothermal method was used to prepare vanadium with a length of about 1μm.VO₂（B）nanorods with a diameter of about100 nm were constructed,and a VO₂（B）based photodetector was constructed.It is found that the VO₂（B）nanorod photodetector has a good optical response in the wavelength range of 450-600nm,especially when the optical power density of the reported VO₂（B）based photodetector is four orders of magnitude lower,the responsivity（R_λ）can still reach 29.6 m A/W.Mo S₂flakes were obtained by mechanical peeling of bulk Mo S₂,and a photodetector based on Mo S₂flakes was constructed.On this basis,VO₂（B）nanorods and Mo S₂thin sheets are stacked by mechanical transfer stacking method to make VO₂（B）/Mo S₂vd W heterostructure photodetector.The photoelectric performance test results show that the dark current is reduced to about 50%of VO₂（B）nanorod photodetector,and the photoelectric current is increased by 2.81 times（about 0.1μA）,R_λIncrease to 205.3 m A/W;The rise and fall time is 56.7/56.8 ms,and the fall time is faster than that of the single VO₂（B）nanorod photodetector（85.1 ms）.The performance improvement of heterojunction photodetectors is due to the formation of type II heterojunction between VO₂（B）and Mo S₂.The built-in electric field at the interface effectively promotes the separation of photogenerated electron hole pairs.In the absence of light,compared with single VO₂（B）nanorods photodetector,the potential barrier formed by the built-in electric field in the heterojunction based photodetector inhibits carrier transport,thereby reducing the dark current.At the same time,a VO₂（B）nanorods flexible photodetector was prepared on a flexible PI（polyimide）substrate,which showed a high photocurrent gain（0.4μA）。（2）On the basis of the above work,by reasonably regulating the content of surfactant CTAB（cetyltrimethylammonium bromide）in the precursor reaction,the hydrothermal method was successfully used to prepare a length of about 20μm.The reaction mechanism of V₃O₇·H₂O nanowire formation was studied.V₃O₇·H₂O nanowires with a diameter of 120 nm.The photodetector based on V₃O₇·H₂O nanowire was constructed.The formation process can be described by the mechanism of"hydration,reduction,stripping,cracking".The research shows that the V₃O₇·H₂O nanowire photodetector has good light response at 300-900 nm under weak light power density,such as under the irradiation of 900 nm wavelength light of 0.7μW/cm²and 5V bias voltage,its R_λUp to 7.3 m A/W,specific detection rate（D^*）up to 4.17×10⁹Jones.On this basis,V₃O₇·H₂O/T_d-Mo Te₂vd W heterojunction photodetectors were fabricated by mechanical stripping,stacking and transfer.Compared with V₃O₇·H₂O nanowire photodetector,the photocurrent of V₃O₇·H₂O/T_d-Mo Te₂heterojunction photodetector is nearly three times higher,R_λand D^*increased by nearly an order of magnitude.The light response and recovery time is27.0/27.2 ms,which is superior to the reported V₃O₇·H₂O based photodetector（0.06 s）.The improvement of heterojunction photodetector performance is due to the built-in electric field formed at the heterojunction interface,which promotes the separation of photogenerated electron hole pairs,and effectively inhibits the recombination of electron hole pairs,thus increasing the photocurrent value.At the same time,a single V₃O₇·H₂O nanowire photodetector was constructed by using photolithography technology.The device has excellent stability;Fast response speed（<68 ms）;Low dark current（2.8 n A）;Good R_λ（420 m A/W）.