First-principles Calculations Of Electrical And Magnetic Properties Of Two-dimensional Layered Semiconductors

Information technology industry has witnessed profound development which brought in new opportunities and challenges to chip designing and manufacturing.Given that traditional silicon-based microelectronic technology is not sufficient to meet the new requirements at the time,developing new alternatives becomes the core of current research.Two-dimensional material is an emerging layered semiconductor nanomaterial.With the features of atomic-level ultra-thin limit thickness and novel physical property,two-dimensional material becomes the hotspots of interdisciplinary research which includes those from the field of physics,chemistry,material science and electronic engineering.In recent years,excellent two-dimensional materials such as black phosphorus and molybdenum disulfide have attracted extensive attention of the scientific community because of their excellent properties related to their special atomic structure.For that reason,we have chosen similar materials which are selenium monosulfide and selenium disulfide as research subjects and adopted adsorption and doping methods to alter their properties.In addition,as a milestone in two-dimensional materials with intrinsic and inductive magnetism,chromium triiodide is the first material that,after reducing the thickness to one atomic layer,still exhibits ferromagnetic ground state.In this thesis,using VASP calculation software that based on density functional theory the structural,electronic and magnetic properties of selenium monosulfide,selenium disulfide,and chromium triiodide are systematically studied.This thesis can mainly be divided into three parts:First,the electronic and magnetic properties of single-layered selenium sulfide and selenium sulfide nanoribbons before and after the adsorption of halogen atoms are studied.After physical adsorption,single-layered selenium sulfide introduces magnetism.When semiconductors certain level of concentration is reached,semiconductor can be transformed into to semi-metal and finally to metal.Second,the electronic and magnetic properties of single-layer selenium disulfide with and without V doping are studied.Simulated calculations were performed for both phases of selenium disulfide.The structures of the 1T phase and the 2H phase both show magnetic introduction to the adsorption.In particular,the structure of the 1T phase shows semi-metallic properties at multiple doping concentrations.In addition,we also conducted research on the changes of the doped structure and the effect of strain on it.The introduction of strain can effectively control the electronic properties of the structure of 1T phase and thus achieve the transition from semimetal to semiconductor.Third,combining the first-principles with knowledge of micro-magnetics,the thesis studied chromium triiodide from different perspectives.The results of the first-principles calculation are transformed into input parameters of the micromagnetic model with an aim to directly predict the macro-magnetic properties of two-dimensional magnetic materials from the perspective of atomic structure without relying on or with little dependence on experiments.The results obtained by the study are in good agreement with all the results from experiments.Therefore,this study provides new ideas and paradigms for the theoretical research of two-dimensional magnetic materials.