Study Of Electromagnetic Properties And Lossless Doping Of Two-Dimensional Semiconductors

As the integration of microelectronic devices continues to increase,the size of individual transistors in integrated circuits will reach the atomic level.Further improvements in device performance will become extremely challenging due to quantum size effects.Spintronics is a new technology that promises to solve the bottleneck problem by simultaneously exploiting the charge and spin properties of electrons to integrate the transmission and storage of information in one device.Room-temperature two-dimensional（2D）ferromagnetic semiconductors are ideal materials for preparing spintronics devices,however,it is very difficult to prepare even in experiments,and the main problem is that the Curie temperature is far below room temperature.Therefore,the search for room-temperature 2D ferromagnetic semiconductors is an important research direction in the field of spintronics.In this paper,the electromagnetic properties,Curie temperature,and magnetic anisotropy energy of 2D Mn₂Se₂ and its derivatives are systematically investigated under external modulation by using first-principles calculations,and it is found that room-temperature 2D ferromagnetic semiconductors can be successfully obtained by suitable edge modifications,and the main work is as follows:The effects of external factors such as strain,external electric field,edge modification and transition metal doping on the electromagnetic properties of 2D Mn₂Se₂ and its derivatives were analyzed.First,trying to modulate the electromagnetic properties of 2D Mn₂Se₂ by applying external strain and electric field.After applying strain,the band gap of 2D Mn₂Se₂ increases（or decreases）linearly with increasing tensile（or compressive）strain.By introducing an external electric field,the 2D Mn₂Se₂ is converted from an antiferromagnetic semiconductor to a metal.It is shown that the external strain and electric field only affect the electrical properties of 2D Mn₂Se₂.Further,the effects of edge modification and transition metal doping on the properties of2D Mn₂Se₂ were investigated.The results show that the 2D Mn₂Se₂ derivatives are transformed into ferromagnetic half-metals by edge modification of Cl,Br,I,S chemical functional groups.The Curie temperatures are 290K,320K,400K,and 1050K,respectively,which are close to or above room temperature.Furthermore,after doping with transition metal Ni,the 2D Mn Ni₃Se₄ is transformed from an intrinsic antiferromagnetic semiconductor to a ferromagnetic semimetal with a Curie temperature of 450 K,which also exceeds the room temperature.Finally,the magnetic anisotropy energies of the 2D Mn₂Se₂ derivatives are all significantly enhanced by edge modification and transition metal Ni doping,in which the magnetic anisotropy energy of the 2D Mn₂Se₂I₂ could reach 1.09 me V/atom.Therefore,2D Mn₂Se₂ and its derivatives have potential applications in spintronics devices.Moreover,for 2D semiconductor devices,the signal transmission rate is often limited by the carrier mobility.Conventional semiconductor doping methods create defects in the crystal structure that cause scattering effects of Coulomb impurities in the conducting channels,which can reduce the carrier mobility in 2D semiconductor materials.In order to improve the signal transmission capability,a novel controlled and non-destructive semiconductor doping technique is proposed in this paper by constructing h-BN/GeSe van der Waals heterostructures.By introducing defects in the h-BN substrate layer adjacent to the GeSe channel layer,charge transfer between the substrate layer and the channel layer can be made,and thus a perfect n-/p-type GeSe semiconductor can be achieved.The main contents are as follows.First,the effects of conventional substitution doping and defect doping on the electrical properties and carrier mobility of 2D GeSe were investigated.It is found that 2D GeSe can be converted between semiconductor and metal by substitutional doping of different atoms,and the carrier mobility varies in the range of 3.45～803.79 cm²V^-1s^-1.At the same time,by introducing defect doping with Ge vacancies,the 2D GeSe still keeps the semiconductor properties unchanged and the carrier mobility is about 705.29 cm²V^-1s^-1.Further,by constructing the h-BN/GeSe heterostructure and introducing boron vacancies in the substrate h-BN layer,a defect state originally located above the Fermi energy level in the band gap moves below the Fermi energy level,i.e.,it is demonstrated that the transition from GeSe to defective h-BN charge transfer,and a defect-free p-type GeSe semiconductor is realized.Conversely,the introduction of a nitrogen vacancy into the substrate h-BN layer resulted in a charge transfer from defective h-BN to GeSe,realizing a defect-free n-type GeSe semiconductor.Among them,the electron mobility of the h-BN/GeSe heterostructure with the introduction of nitrogen vacancies can be as high as 1678.14 cm²V^-1s^-1.Compared with the conventional doping method,the carrier mobility of the heterostructure doping has been significantly improved.Therefore,the heterostructure doping method in this paper can not only realize lossless n-/p-type 2D semiconductor materials,but also maintain the high carrier mobility in their channel layers,which provides a theoretical basis for realizing 2D semiconductor spintronic devices with high-speed transmission.