Study On The Electronic Structure And Magnetic Properties Of Ca₂Ge-based DM

With the device size and fabrication cost predicted by Moore’s Law approaching the limit,the development of novel spin-coated devices with immediate application prospects is critical.Diluted magnetic semiconductors with electronic degrees of freedom that can control both spin and charge at the same time are indispensable.Therefore,it is a meaningful work to explore and develop new dilute magnetic semiconductors（DMS）.Based on this,the first-principles calculations were used in this paper to analyze the effects of different magnetic elements,rare earth elements,and Mn doping on the electronic structure and magnetic properties of Ca₂Ge-based dilute magnetic semiconductors.The main research contents and conclusions are as follows:（1）The stability,electronic structure and magnetic properties of the Ca₂Ge system doped with V/Cr/Mn with different Ca atomic sites were calculated and analyzed.The systems in which V/Cr/Mn was incorporated into the Ca II atomic site had relatively stable structures.At the same time,the V/Cr doping led to the transformation of the Ca₂Ge system from semiconductor to semi-metallic property,while the system after Mn doping was still a direct bandgap semiconductor,and the bandgap increased.In addition,the incorporation of V/Cr/Mn made the Ca₂Ge system introduce impurity energy levels,resulting in a net magnetic moment and external magnetic properties;the magnetic moment of the Mn-doped system was the largest.（2）The calculated results of electronic structure and magnetic properties of La/Ce/Nd doped Ca₂Ge system showed that the Ca₂Ge system doped with Ca II atomic sites by three rare earth elements has a more stable structure.Based on this result,it was found that La/Ce/Nd doping introduced impurity levels.The difference was that the system was still a direct bandgap semiconductor after La doping,and no net magnetic moment was generated;the direct bandgap semiconductor with magnetic properties was formed after Ce doping;and the introduction of Nd makes the system form a spin polarizability.It was a 100%semi-metal and has the strongest magnetic moment,which was a good material for controlling the charge and spin properties of Ca₂Ge-based DMS.（3）The electronic structures and magnetic properties of three Ca II atomic sites doped with different Mn concentrations were calculated.The research showed that with the increase of doping concentration,the Ca₂Ge system transforms from semiconductor to metal,magnetic semiconductor and semi-metal in turn;and the size of magnetic moment was not proportional to Mn doping concentration.Therefore,we can tune the properties of Ca₂Ge-based DMS by changing the concentration of Mn atoms doped with Ca₂Ge.