Electrical Transport Properties Of Two-dimensional MoS₂ And CsPbBr₃ Devices Based On Strain Engineering

Two-dimensional materials have gained popularity among scientific researchers for their excellent physical and chemical properties.Two-dimensional molybdenum disulfide（MoS₂）and cesium lead bromide（CsPbBr₃）are two typical semiconductors with tunable band gaps,which makes them promising for applications in electronic devices.However,the performance of 2D materials is greatly influenced by factors such as the number of layers and defects,and the optoelectronic properties of intrinsic2D materials need to be improved.Studies have shown that strain engineering is an effective means to enhance the device performance of 2D materials.Therefore,this paper investigates the current-voltage performance of layer less 2D MoS₂ and 2D CsPbBr₃ nanosheet devices with different thicknesses based on strain engineering to further explore their applications in future electronic devices.The main research of this paper is as follows:1.2D MoS₂ and 2D CsPbBr₃ nanosheets were prepared using CVD and liquid-phase synthesis,respectively.Then the morphologies were characterized by OM,SEM,and AFM,and their physical phases were characterized by Raman spectroscopy and X-ray diffraction.The devices based on two-dimensional MoS₂ and CsPbBr₃ were constructed by using conductive AFM.2.The MoS₂ was transferred to the patterned substrate by the wet-assisted transfer method to form the constrained strain.The change of its surface potential was then tested based on the KPFM module,and it was found that the CPD magnitude at the edge of the slot decreased by month 94 m V relative to the center of the slot.therefore,we further used C-AFM tests to obtain the local Ⅰ-Ⅴ characteristics of MoS₂ at seven different points on the rectangular slot,and the results showed that the conductivity of MoS₂ was greater near the edge of the slot.The distribution of MoS₂ strain was determined using Raman surface sweep and finite element simulations.Finally,the rate of change of the seven-layer MoS₂ energy band with strain was obtained based on DFT calculations to be about-103 me V/%.The experimental conductivities of MoS₂ at different strains matched well with the theoretical value,which proved that the strain reduced the energy band of MoS₂ and thus enhanced its conductivity.3.Electrical properties of two-dimensional CsPbBr₃ of different thicknesses under different strains.The magnitude of the strain applied to the samples under different tip loads was calculated using the Hertzian model.The Ⅰ-Ⅴ characteristic curves of 12 nm,17.5 nm and 22 nm thick CsPbBr₃ at loads of 10 n N,20 n N and 30n N were tested based on conductive AFM by applying strain to the sample through the AFM tip,and the Ⅰ-Ⅴ characteristics were enhanced with increasing load.We then calculated their Schottky potentials at different strains using a hot electron emission model.The results show that the Schottky barrier decreases for all samples as the strain increases,and the thinner samples have a correspondingly smaller Schottky barrier,showing a better electrical response.Then we tested the piezoelectric properties of three samples based on PFM and obtained the vertical piezoelectric coefficients of 12 pm/V,9 pm/V,and 3 pm/V for 12 nm,17.5 nm and 22 nm thick CsPbBr₃,respectively.Finally,based on the theory of piezoelectric optoelectronics,it is explained that the decrease in Schottky barrier due to increasing load is due to the charge polarization caused by the piezoelectric effect.