Study On The Surface And Interfacecharacteristics Of 2D Van Der Waal Heterojunction Photodetectors

Two-dimensional materials(2DMs)have attracted attention tremendous due to their excellent optical absorption,high electron mobility and good heat conduction.In particular,they perform a good prospect in the application of photoelectric detection.Compared with the traditional bulk materials,they have a better performance in flexibility and transparency caused by their ultra-thin thickness.Meanwhile,the band gap of 2DMs can span over a wide energy range.In addition,the spatial stacking of 2D layered materials can combine the excellent characteristics of different materials to achieve the atomic level functional integration,which is particularly promising for the development of integrated circuits,wearable devices,and other fields.TMDs(Transition Metal Dichalcogenides)have many excellent properties,such as bandgap adjustable,good optical absorption and so on.Graphene has excellent photoelectric properties,such as wide spectral absorption range,high carrier mobility and so on,which make it a promising candidate to be employed in the field of photoelectric detection,especially for the realization of wide spectral detection.In this paper,three representative 2DMs(i.e.molybdenum telluride(Mo Te₂),molybdenum disulfide(Mo S₂)and graphene)are selected as the research samples.In this work,fabrication,improvement and characterization of heterojunction structure are discussed.We firstly focus on the study of the photoelectric and heterojunction interface characteristics of the 2D heterojunction photodetector and the in-depth analysis of the intrinsic working mechanism.Then,the factors affecting the performance of the device are summarized.Finally,a feasible optimization scheme is proposed.The device preparation process,performance characterization,mechanism research and other aspects in this work can constitute a significant step towards the follow-up work.The main research contents and results are as follows:(1)To explore the preparation process of 2DMs photodetector,PDMS(Polydimethylsiloxane)was used to improve the material preparation and electrode transfer process.A new rapid and repeatable device preparation process was introduced.The process simplifies the traditional device preparation process and improves the success rate of device preparation,which provides more possibilities for rapid and efficient device preparation.(2)The self-driving photodetector of Mo Te₂/Mo S₂heterojunction is designed and fabricated.The internal working mechanism is analyzed and the reasonable optimization scheme is proposed.In this paper,we have successfully fabricated a Mo Te₂/Mo S₂heterojunction self-driving photodetector,based on the improved rapid device preparation process.Based on the vertical heterojunction structure,the photodetector realizes the self-driving function through the photovoltaic effect brought by the built-in electric field,which is of great significance for the application of 2DMs in low power consumption and energy saving.In the range of laser power,the highest R of the device is about 7.32×10^-3A/W,D^*is about 1.25×10⁷Jones,and it can work stably.This shows that the rapid fabrication process of the devices used in this paper can achieve rapid and efficient preparation of high-performance heterojunction photodetectors,which has high practical value.Based on the photoelectric test results of the device,the carriers'behavior of the heterojunction surface is analyzed,the internal working mechanism of the photodetector is deeply understood,the possible factors affecting the performance of the device are discussed,and the methods of improving the performance such as reasonably controlling the material thickness and optimizing the interface quality are put forward,which will lay the foundation and provide ideas for further research.(3)A wide-band photodetector with p-g-n structure was designed and fabricated.The mechanism of the photodetector is analyzed and a reasonable scheme is proposed.Because of the bandgap limitation,2DMs work in visible and near-infrared band,which greatly limits their practical application.The p-g-n structure photodetector extends its detectable band range by inserting graphene with zero bandgap,and realizes the rapid separation of photogenerated electrons and holes through built-in electric field,improves carriers'life,reduces dark current,and improves device performance,which is of great significance to the research of wide band detection function of photodetector.In this paper,Mo Te₂/graphene/Mo S₂heterojunction photodetectors have been fabricated based on the rapid device preparation process,and their photoelectric properties have been tested.The device has successfully measured the light response at 532 nm and 1550 nm,respectively.It shows that the photodetector can expand the detection band of the detector and has high application value.Through the analysis of the photoelectric test results of the device,combined with the photocurrent space scanning,it is concluded that the optical response in the near-infrared range of the device mainly comes from the heterojunction region.The results show that the R of the device can be continuously adjusted by adjusting the external bias and laser power,which is conducive to better device performance in the application process.Finally,the influencing factors of device performance are summarized,and reasonable optimization methods such as improving the thickness of graphene are proposed,which will lay a foundation for further research and provide ideas.