Synthesis And Optoelectronic Properties Of Mixed Dimension Van Der Waals Heterostructures

The discovery of graphene has attracted intense interest in two-dimensional（2D）layered materials.2D materials with atomic thickness exhibit novel quantum properties which cannot be observedb in bulk materials,such as indirect-to-direct band gap transition,high field effect and strong exciton coupling.However,single2D materials still have various problems,such as extremely low optical absorption coefficients due to the ultra-thin thickness and difficulty in achieveing room-temperature ferromagnetism.Mixed-dimensional van der Waals（md-vd W）heterostructures which combines 2D materials with non-2D materials（quantum dots,nanowires and bulk materials）show remarkable electronic,magnetic and optoelectronic characteristics.For example,2D material/quantum dot heterostructure detectors show huge optical enhance.2D materials/ferromagnetic metals have spin-valve effect.From the realization of many md-vd W heterostructure,the md-vd W heterostructure provides possibility to develop novel devices,which has important application and theoretical significance.In this thesis,kinds of md-vd W heterostructure waere synthesized and the optical and electrical properties were studied.（1）A general approach to control the growth of TMDCs/XN heterostructures by using the lattice symmetry of transition metal chalcogenides（TMDCs）is proposed.XN represents a class of antiferromagnetic metals and semiconductors,such as Co S and Cd S.The kinetics of epitaxial growth of XN nanosheets induced by TMDCs is also investigated by first-principles calculations,which provides theoretical basis for the epitaxial growth of large-area TMDCs/XN heterostructures.（2）The singular electrical coupling effect between the bands of two kinds of md-vd W heterostructures is studied.（a）The Mo(S_xSe_1-x)₂/Cd S_xSe_1-xheterostructure forms a type II band.The photogenerated holes transfer to Mo(S_xSe_1-x)₂,and the electrons on Mo(S_xSe_1-x)₂ have more chances to transition to the valence band,resulting in an over 10⁵times luminescence enhancement（b）The all-light-controlled neuromorphic optical memory is realized by the surface defect formed by the adsorption of O₂ on the surface of the Sr Ti O₃/graphene heterostructure and the heterostructure interface energy band.（3）Based on the synthesis of TMDCs/XN and Sr Ti O₃/Pb S heterostructures,the influence of the physical and chemical properties of the substrate surface on the nucleation density is clarified.The variation principle of the crystallinity of the epitaxial layer under the synergistic effect of the growth temperature,the substrate surface structure and the growth time is proposed.The method for batch preparation of centimeter scale,highly oriented,polycrystalline and short wave infrared sensitive Pb S thin films on Sr Ti O₃ substrate is obtained.The relationship between the crystallinity and the response speed of Pb S thin films is further investigated,showing application potential in the development of large area Pb S focal plane detector arrays.In summary,a general strategy for synthesizing a class of md-vd W heterostructure is proposed.Controlling mechanism of interface coupling on the growth of epitaxial layer is proposed.Singular optical and optoelectronic properties attributing to interface coupling are discovered.Further researchs on the influence of two-dimensional material surface structure on large-area semiconductor epitaxial growth and singularphotoelectric characteristics and optoelectronic applications of md-vd W heterostructure are expected.