Study On Two-dimensional Semiconductor And Its Electro-optic Characteristics

Two-dimensional semiconductor materials,such as graphene,transition metal sulfides,black phosphorus,boron nitride and so on,have been widely used in integrated optoelectronics because of their unique electrical and optical properties.In these two-dimensional semiconductor materials,the direct band-gap semiconductor black phosphorus fills the gap between graphene and transition metal sulfides,and shows anisotropy and selectivity to light.In addition,black phosphorus has high hole mobility,up to 1000 cm²V^-1s^-1,showing excellent transistor characteristics.This series of advantages has set off an upsurge in the research of optoelectronic detection devices based on black phosphorus.However,in practical application,because two-dimensional semiconductor material is a kind of material with atomic layer thickness,the absorption of light is very weak,which is not conducive to light detection,so it is necessary to design a new device structure to improve the interaction between black phosphorus and light.As we all know,silicon waveguide technology has been widely used in optical transmission.In order to ensure low transmission loss,for conventional optical transmission problems,especially in bending,large size bending radius is usually used to obtain high optical transmission efficiency.However,how to reduce the device size and facilitate device integration while ensuring low optical transmission loss is also one of the key problems solved in this paper.In view of the small size and high transmission efficiency,a photonic crystal mirror transmission structure based on two-dimensional semiconductor material black phosphorus is designed in this paper,and the device size is effectively reduced while the reflection efficiency at the bend is enhanced.For the electrical properties of two-dimensional semiconductors,in addition to graphene because of its zero band gap,other two-dimensional semiconductor materials,such as MoS₂,of transition metal sulfide family,have semi-gold properties.High contact resistance is produced due to the mismatch of the material itself in the process of growth and fabrication,which has become one of the main bottlenecks in the development of high performance MoS₂ optoelectronic devices.At present,the purpose of the report on this problem is to start with the research of the material itself,such as doping,adjusting the phase transition of the material,etc.,but there is a lack of systematic and in-depth research on the influence and causes of the process on the material and the device in the fabrication process of the device.In addition,compared with the traditional bulk semiconductor,two-dimensional semiconductor,as a layered material,can be placed on any substrate,so it can realize photoelectric detection with a variety of device structures.Because of its adjustable band gap,strong carrier mobility and flexible system integration,black phosphorus has done a lot of work in broadband photodetector based on black phosphorus,and has become one of the most studied optoelectronic devices at present.However,most of the research focuses on the structure of phototransistors,such as the construction of different shapes of device electrodes and the different stacking of the same materials,and so on,but there is a lack of relevant research on the noise problems existing in these structures.The existence of device noise has seriously affected the sensitivity of device detection.Therefore,the methods to reduce device noise need to be further studied and reported.For the above problems,this paper studies four aspects based on two-dimensional semiconductors and their electro-optic characteristics.Firstly,the photonic crystal waveguide structure is designed,and the optical absorption of black phosphorus in two-dimensional semiconductor material is studied.Then,the compact photonic crystal mirror structure based on black phosphorus is designed,and the optical transmission efficiency is studied.Subsequently,graphene/MoS₂ heterostructures were prepared experimentally,and the effects of oxygen plasma and annealing process on materials and devices were analyzed in detail.Finally,graphene/h-BN/BP heterojunction photodetector was prepared by reducing noise,and the photoelectric response mechanism and noise mechanism were deeply studied.The detailed research content and results are as follows:1.In order to solve the problem of weak absorption of light by black phosphorus in two-dimensional semiconductor materials,a photonic crystal waveguide structure which can enhance the absorption of black phosphorus is designed by using the photonic band gap effect of silicon-based photonic crystal structure.In this numerical analysis,the transmission spectrum of light in PCW structure based on black phosphorus is studied by using finite difference time domain?FDTD?numerical method,and the absorption rate of black phosphorus to light is calculated.By optimizing the structure parameters,it is found that the photonic crystal waveguide structure based on black phosphorus can effectively enhance the interaction between black phosphorus film and light,and the optical absorption performance of black phosphorus film can be improved,and the absorption rate of black phosphorus is36.8%at 1550 nm.2.Based on the study of black phosphorus and photonic crystal structure,an ultra-compact photonic crystal mirror structure based on black phosphorus is designed innovatively.In this paper,black phosphorus thin films are acted on photonic crystal mirrors to form 90°curved waveguides,and the reflection efficiency of light passing through photonic crystal mirrors is studied.The mirror size at the bend is less than 5?m×5?m,and the super compact type is realized.In addition,in order to reflect the excellent difference of this design,a variety of curved waveguides with various structures are also designed under the same size.It is found that the super compact photonic crystal mirror structure based on black phosphorus achieves the strongest reflection at the bending point.When the incident light is incident in TE mode,the reflection efficiency can reach 94%at 1550 nm.3.Graphene/MoS₂/Ti/Au structure with high contact performance was obtained by using graphene semi-gold property as MoS₂ electrode.Compared with conventional MoS₂ devices,the devices in this paper benefit from the improvement of contact materials.In this paper,two kinds of process steps,including oxygen plasma etch treatment and annealing process,were studied,and the effects of doping on the properties of materials and devices were studied by Raman spectroscopy and XPS.It is found that the combination of the two-step process can not only etch the material at the channel,but also improve the impurities introduced by the device in the etch process,and finally obtain relatively low contact performance.The contact resistance of 35.7?·mm is obtained.4.Based on the research results that graphene is used as electrode to obtain high contact performance,the photodetector based on low noise is studied at the end of this paper,and graphene/h-BN/BP vdW Heterojunction photodetector is fabricated.Compared with BP phototransistors,the heterojunction devices in this paper benefit from the insertion of h-BN tunnel barrier layer,which significantly prevents the dark current fluctuation caused by shallow trap center.The low noise graphene/h-BN/BP vdW heterojunction photodetector is realized.The device has high photoelectric detection performance in medium wave infrared,the maximum optical response is 40?AW^-1,and the detection rate is 1.02×10⁹ Jones.In addition,compared with BP phototransistor,the sensitivity of the device is more than 100times higher,which can be attributed to tunnel aided noise management.This new technology not only provides an attractive platform for the practical application of long wavelength optoelectronic detection,but also opens up a new way to control noise.