Study On Photoelectric Characteristics Of Two-dimensional Bi₂Se₃/MoSe₂ Van Der Waals Heterojunction

Two-dimensional materials have become the focus of research in the field of low-dimensional materials in recent years due to their rich physicochemical properties,diverse preparation methods,and ease of tuning.These two-dimensional materials usually do not have dangling bonds on their surfaces,so it is easy to construct two-dimensional van der Waals heterostructures that take advantage of two or more two-dimensional materials,opening a new path for the development of photosensitive devices for optoelectronics,biomedicine,fiber lasers,photodetection,and hyperspectral imaging.Firstly,a double-layer Bi₂Se₃/Mo Se₂van der Waals heterojunction is constructed.Combined with the first principle based on density functional theory,the band structure,charge distribution,density of States and other properties of the heterojunction are calculated and predicted.We found that the strong spin orbit coupling of Mo Se₂and Bi₂Se₃enhanced the Zeeman and Rashba splitting of the band after the formation of heterojunction.External electric field,stress and twist angle are effective means to regulate the electronic characteristics of heterojunction.Our calculations show that these modulation methods will change the band alignment from type II to type III or even type I,and also change the band gap type of heterojunction from indirect to direct.According to the calculation results of optical properties,the infrared absorption of heterojunction is 2-6 times higher than that of monolayer Bi₂Se₃and two orders of magnitude higher than that of monolayer Mo Se₂.Secondly,this paper investigates the preparation of two-dimensional Mo Se₂and Bi₂Se₃on Si O₂/Si substrates by CVD method and optimizes the process parameters such as the carrier gas flow rate.The characterization methods such as optical microscope,Raman,EDS and AFM proved that CVD method can be used to prepare high quality two-dimensional Mo Se₂and Bi₂Se₃single crystals with sizes over 200?m and 70?m respectively.In particular,the CVD for growing two-dimensional Bi₂Se₃,which is less studied at present,is explored.The two-dimensional Bi₂Se₃prepared by this method exceeds most of the current research in area and crystal quality.Finally,two-dimensional Bi₂Se₃was successfully epitaxially grown on the surface of two-dimensional Mo Se₂by using more optimized growth parameters.Compared with the wet transfer,which is the most widely used method for preparing two-dimensional van der Waals heterojunction,epitaxial heterojunction has higher preparation efficiency and cleaner interface.Finally,the two-dimensional Bi₂Se₃,Mo Se₂and Bi₂Se₃/Mo Se₂van der Waals heterojunction phototransistor devices were prepared in this paper using the micro-nano process.The I-V characteristics of these devices and the photoelectric response characteristics under the conditions of different wavelength,different bias voltage and different optical power density are tested respectively.The test data show that the Bi₂Se₃/Mo Se₂van der Waals heterojunction phototransistor achieves 1260 A/W and 3.3×10¹²Jones in responsivity and detectivity under 980nm light irradiation,respectively.The device's response wavelength range of 405-1940 nm validates the results of first principles calculations,it can be proved that Bi₂Se₃/Mo Se₂van der Waals heterojunction device has a wider spectral response range compared with the devices of two discrete materials.In the future,it can be used for wide spectral detectors and image sensors from visible to short wave infrared light.