Study On Anisotropy And Strain Regulation Of Twodimensional Germanium Selenide

Two-dimensional（2D）materials such as graphene and transition metal dihalides（TMD）exhibit excellent out-of-plane optical anisotropy due to their strong in-plane covalent bonds and weak out-of-plane interactions.However,the optical axes of these2D materials are usually the out-of-plane axes,which make it difficult to have greater anisotropy in both in-plane and out-of-plane directions.Therefore,Germanium selenide（GeSe）as a 2D material has attracted much attention from researchers because of its excellent air stability and in-plane anisotropic lattice structure.This in-plane anisotropy not only adds a new dimension to the properties of 2D materials,but also stimulates the development of angular resolution Photonics and electronics.Because these highly in-plane anisotropic structures are highly coupled with many unique physical properties of GeSe,strain engineering can be used as a simple and feasible means to control GeSe anisotropy,which opens up new possibilities for its application in the fields of mechanical and photoelectric.This paper focuses on the anisotropic photoelectric properties of GeSe nanosheets and the anisotropic phonon response under strain engineering.The main research contents include:1.The atomic structure of GeSe was characterized by high-angle annular dark field of transmission electron microscopy,which confirmed that the peeled GeSe nanosheets aligned in the direction of armchair and zigzag.The crystal orientation of GeSe was judged by combining selected electron diffraction and angular resolution Raman spectroscopy.We found that the direction of maximum and minimum Raman intensity of Ag mode in the initial angular resolution Raman spectrum can be used to calibrate the armchair and zigzag directions of GeSe,respectively.Angular-resolved Raman spectroscopy was used to characterize GeSe with different thickness.It was found that thickness affects the anisotropy of phonon response.These results provide a more convenient way to judge the crystal orientation of GeSe.2.The phonon response of GeSe under uniaxial tension strain is systematically studied by Raman spectroscopy.It is found that the red shift of B_3g and A_g~3 modes can be clearly observed when loading uniaxial tension strain along armchair direction,while the blue shift of B_3g and A_g~3 modes can be clearly observed when loading strain along zigzag direction.First principles reveal that the anisotropic phonon response in GeSe is due to changes in bond length and angle due to uniaxial tension strain.Simulations using angular resolution Raman spectroscopy and Raman formula show that the anisotropy of A_g mode is highly coupled with the strain.When strain is loaded,it causes|c/b|to increase,further causing the A_g~3 mode to change from elliptical to dumbbell and the Raman intensity to increase.In addition,the band gap and polarization intensity can be controlled by strain according to the first principle.The above results show that strain engineering can be used as a more convenient method to adjust the anisotropic lattice of GeSe and lay a foundation for its physical properties.3.In this paper,a GeSe-based in-plane two-terminal device and a three-terminal transistor are designed,and two electrodes are prepared in the armchair and zigzag directions of the device.The performance of the device in different directions is systematically characterized,and the optical and electrical properties of the anisotropy are investigated.GeSe-based devices not only have high photoelectric response,but also exhibit stable cyclic properties.The results of electrical transport properties show that GeSe exhibits the properties of P-type semiconductors,and its electrical properties exhibit anisotropy with the applied direction of the electric field.When the electrodes follow the zigzag direction,typical transistor characteristics are displayed in the range of V_ds>0,and the channel of GeSe devices can be controlled.When the electrodes follow the direction of armchair,leakage occurs and the transistor characteristics are not reflected.Finally,we have achieved the regulation of electrical transport performance by strain.These studies provide a basis for the development of new optoelectronic devices based on the physical properties of GeSe anisotropy.