| Photodetectors are an important part of many optoelectronic equipment and systems,and have important applications in photoelectric imaging,optical communications,biomedicine,environmental monitoring,security inspection,military and other fields.Traditional semiconductor materials,such as Si,Ge,In Ga As,Hg Cd Te,etc.,are widely used in photodetectors.However,photodetectors based on traditional semiconductor materials have problems such as large dark currents and difficult to be applied to flexible optoelectronic devices,which limit their further applications.With the increasing demand for high performance,wide spectrum,non-refrigeration and flexibility of photodetectors,it is of great significance to explore and develop photodetectors based on new semiconductor materials.Compared with traditional semiconductor materials,two-dimensional semiconductor materials have very excellent optical,electrical and mechanical properties,and have ultra-thin thickness.Photodetectors based on two-dimensional semiconductor materials and their heterojunctions have caused interest in recent years.Two-dimensional semiconductor materials are stacked through Van der Waals interaction between layers to form a heterojunction.This heterojunction can combine the properties of different materials and has great research value and application prospects.Among them,the photodetector based on the vertical heterojunction of the two-dimensional semiconductor material can effectively suppress the diffusion current through the built-in electric field formed by it,thereby reducing the dark current,and can effectively separate the photo-generated electron-hole pairs under the built-in electric field,thereby improving the photoresponsivity.Because of the interlayer transition in the type II band structure,the response wavelength can be effectively expanded.At present,the research on two-dimensional semiconductor photodetectors is mostly focused on a single two-dimensional material system.The electrical and photoelectric characteristics of Van der Waals heterojunction devices constructed from two or more two-dimensional semiconductors and the physical mechanism of photodetection need to be further studied.This paper mainly studies the photodetector based on the vertical heterojunction of two-dimensional semiconductor materials,and selects MoTe2,MoS2,BP,and b-AsP as the two-dimensional semiconductor unit to construct the Van der Waals heterojunction.Through continuous improvement of the device structure design and manufacturing process,it has been successfully developed vertical heterojunction photodetectors,and the photoelectric mechanism of the photodetector was discussed and analyzed,and more complex p-n-p type device was constructed on this basis.The main research content and results of the paper are as follows.（1）Systematically master the preparation process,characterization means and test methods of two-dimensional semiconductor photodetectors,through mechanical exfoliation,dry transfer,ultraviolet lithography/electron beam exposure（EBL）,magneto-controlled sputtering,metal peeling and wire bonding to complete the device preparation;the heterojunction is characterized by atomic force microscopy（AFM）and Raman spectroscopy;the responsivity of the photodetector is determined by electrical testing under illumination and dark condition.（2）The MoTe2-MoS2 photodetector was developed,and the device was characterized and tested.The results have shown that the rectification ratio of the MoTe2-MoS2 device can reach up to 2.53×102,indicating that the two materials form a p-n junction and have good rectification characteristics;under zero bias,the dark current of the device is about 10-11A level,photocurrent is about 10-6 A level,photoresponsivity switch ratio is about 105,which can realize photovoltaic self-driving detection;photocurrent is mainly generated at zero bias voltage and reverse bias voltage,and the maximum can be inμA magnitude,the photocurrent area is at the p-n junction area formed by the two materials;when Vsd=0,the photoresponsivity ofλ=532 nm can reach up to 110.6 m A/W,and the photo-responsivity ofλ=1064 nm can reach up to 9.2m A/W.It has reached up to the advanced level of similar devices and has certain application prospects in the field of photoelectric detection.（3）BP-MoS2 and b-AsP-MoS2 vertical heterojunction devices were developed,and the devices were characterized and tested.According to the test results,the rectification ratio of the BP-MoS2 device is 9.66×102 and the rectification ratio of the b-AsP-MoS2device is 60,indicating that the p-n junction is well formed in the two types of devices and has better rectification characteristics;Under zero bias,the dark current of the device is as low as 10-12 A;when Vsd=-2 V andλ=532 nm,the photoresponsivity of BP-MoS2 and b-AsP-MoS2 devices is on the order of m A/W.The results in this chapter reflect the research value of BP-MoS2 and b-AsP-MoS2 devices in the field of photodetection.（4）The MoTe2-MoS2-MoTe2 photodetector was developed,and the devices were characterized and tested.It can be seen from the results that the devices have photocurrent under forward and reverse bias voltages,and the maximum can be in the order ofμA;when Vsd=-2 V,λ=532 nm,photoresponsivity can reach to 219.7 m A/W.The results in this chapter reflect that the construction of a p-n-p or n-p-n three-layer heterojunction is expected to further improve the responsivity of the two-dimensional semiconductor photodetector. |
