Monolayer MoS₂ Crystal Growth And Doping By Chemical Vapor Transport

Two-dimensional transition metal chalcogenides（TMDCs）have a significant chemical composition and crystal structure,which endow them with rich physical and chemical properties and broad application prospects and pose challenges for the controllable synthesis of materials.At present,the crystal quality of two-dimensional materials obtained by the mechanical exfoliation method is good,but the shape and number of layers are not controllable.Physical vapor deposition（PVD）and chemical vapor deposition（CVD）have poor crystallization quality and universality.In order to settle the shortcomings of traditional two-dimensional material growth methods,the chemical vapor transport（CVT）method is used to synthesize two-dimensional MoS₂crystals in a high vacuum sealing environment.As a result,the synthesized crystals have high crystallization quality and higher applicability.TMDCs with a single molecular layer has unique electronic structures and excellent electrical properties and have significant application prospects in microelectronic devices and optoelectronic devices in the visible light band.However,the single molecular layer’s low absorption coefficient and defects affect luminous efficiency and photoelectric performance.By introducing external defects,the electronic energy level can be enriched,and the optical and electrical properties of monolayer TMDCs can be significantly improved.It has far-reaching significance in preparing efficient optoelectronic devices and high mobility FETs.The main research contents of this paper are as follows:1)MoS₂ formed the representative of TMDCs materials to grow two-dimensional MoS₂ crystals by the CVT.The effects of various reaction conditions in the growth process of the CVT method on the growth results were analyzed and studied.Comprehensive characterization methods of various existing structures and properties confirmed that the two-dimensional MoS₂ crystal prepared by this method has high quality and good controllability compared with the traditional growth method.2)The one-step method of MoS₂ crystals was doped with IVB group transition metal elements.The introduction of exterior defects enriched the electronic energy level structure of MoS₂ itself to improve the photoluminescence and electrical properties of single-layer MoS₂ crystals.The primary characterization methods prove that MoS₂ is a single molecule layer,and the doping elements are successfully incorporated into the lattice of MoS₂ crystal,realizing the in-plane doping of MoS₂crystal and the enhancement photoluminescence and the improvement of electrical properties of MoS₂.3)The rare earth elements Gd and Dy were doped into MoS₂ crystal by the one-step method.The band structure of MoS₂ was changed by using the rich electronic energy level of rare earth elements.It finds that the fluorescence of MoS₂significantly enhances after Gd doping.Moreover,the carrier lifetime was significantly prolonged by the kinetic test.In this work,the luminescence properties of MoS₂ thin film are greatly improved by doping foreign impurity atoms,and the n-type conductivity of MoS₂ is improved to a certain extent,which is of great significance for further study of MoS₂ thin-film optoelectronic devices and field-effect transistors.