The Modulation Of Optical And Electrical Properties Of Two-dimensional Tungsten Diselenide Via Doping

Two-dimensional transition metal chalcogenides（TMDCs）have excellent optical,electrical and mechanical properties.As an ideal material for new electronics optoelectronics devices,TMDCs play a crucial role in the field of device size miniaturization,quantum information science and optoelectronics.However,the fabrication of electronic and optoelectronic devices based on TMDCs inevitably lead to a formation of Schottky contact at the the metal-semiconductor interface.The high Schottky barrier between pristine TMDCs and metal severely limits the performance of devices,such as low carrier mobility,high contact resistance and so on.With the rapid development of modern electronic technology,the performance of pristine TMDCs is increasingly unable to meet the needs in practical application.Therefore,it is particularly important to regulate the properties of TMDCs materials.At present,doping engineering and defect engineering are commonly used strategies to modify the performance of TMDCs.The optical and electrical properties of two-dimensional TMDCs can be easily controlled by surface modification and doping due to their ultra-thin atomic thickness and ultra-high surface volume ratio.In addition,the lattice of TMDCs may contain various structural defects,such as vacancies,impurities and adsorbed atoms,which also have a great impact on the optical and electrical properties of two-dimensional TMDCs materials.Therefore,it has become a focus in the field of materials science to realize the precise customization and regulation of their properties through various modification and doping methods.If the performance of TMDCs materials can be effectively and flexibly regulated,it is bound to provide a great boost to the technological innovation in the field of material application,and further promote the integration of small devices and the high efficiency of device performance.This paper is mainly based on the spectral characterization of electron beam irradiaton and potassium surface modification doped WSe₂and the application research of field-effect structure devices.The specific research contents are summarized as follows:1.Controllable n-type doping was realized in WSe₂ monolayers by means of electron beam irradiation,which significantly improves the electrical performance of WSe₂ field effect transistor.Electrical properties characterization indicate that this method can significantly increase the electron mobility and electron concentration in WSe₂ field effect transistor.Upon treatments,the source-drain current and the electron mobility of back-gated monolayer WSe₂is enhanced by an order of magnitude and 8 times respectively,and the electron concentration increases from 1.17×10¹¹ cm^-2 to 5.32×10¹¹ cm^-2.The quenching of the photoluminescence（PL）intensity and increase of trion weight further verify the realization of efficient n-type doping.While no obvious changes are found in Raman spectra after irradiation treatment,which indicates the integrity of the lattice structures.By characterizations of PL spectra at low temperature,the n-type doping is empowered by the formation of Se vacancies.The generation of a moderate amount of Se vacancies contributes to the increase in probability of charge hopping transport and the shift of Fermi level towards conduction band,which induces the thinning of the width of the Schottky barrier between metal and WSe₂.Thus,the electrical performance of WSe₂ field effect transistor is improved significantly.Moreover,by adjusting the electron beam irradiation dose and irradiation region,controllable doping with high precision can be realized in WSe₂.This work provides a reliable method for the realization of high performance electronic and optoelectronic devices by utilizing lattice defects in TMDCs rationally.2.Potassium surface modification was used to improve the electrical properties of WSe₂monolayer field effect transistor in the way of surface charge transfer doping.The experimental results show that the electron mobility of the device is increased to 17.1cm²V^-1s^-1 and the electrical conductivity is increased by 6 orders of magnitude at a potassium thickness of 0.2 nm.The softening of E₂¹ _g and A_1g phonon mode in Raman spectrum indicates that a large number of electrons are transferred into WSe₂ after surface modification of potassium,and the electron phonon coupling is enchaced,resulting in a wider peak deformation.Moreover,theA_1g mode is more sensitive to the doing as compared to the E₂¹ _g mode.The decrease of PL intensity and the red shift of peak position indicate that a large number of electrons in WSe₂ are closely bound to the neutral excitons to form charged excitons,which inhibits the radiative recombination of the neutral excitons.The promoted electrical performance is due to the improvement of the Schottky contact between the metal and WSe₂ and the gradual transition to ohmic contact as well as the transition from semiconductor phase to metallic phase of WSe₂.Through the analysis of the optical and electrical measurements results,it can be concluded that potassium surface modification can be used as a controllable and effective doping strategy to regulate the optical and electrical properties of two-dimensional TMDCs materials,which is expected to be applied to the preparation of high-performance TMDCs electronic devices.