Theoretical Studies Of The Quantum Manipulation And Application Towards Single Defect In Semiconductor

The development of material science and physics continuously promote the rapid progress of basic science research and electronic science and technology.The revolutionary development of information technology,which is closely related to people's lives,is inseparable from the leap in the quality towards the research of the quantum theory and of semiconductor materials.The key point is that people are able to make use of the basic atomic,molecular and electronic properties in microscopic dimension and to make good design of new materials to give good development of new electronic devices.As for majority of new material research,the further investigation of the electron spin polarization properties has led to the realization that electron spin in semiconductor can be optical manipulated by introducing single defect states,such as point defect states and point-doping states,into semiconductor materials.And the satisfactory conductivity and catalytic activity are able to be achieved by controlling the local charge distribution of the material system.At present,the quantum spin control research of materials has induced wide interest around the scientific world.The main topic is the color center in solid-state semiconductor:negative-monovalent charged nitrogen-vacancy complex in diamond,silicon vacancies in silicon carbide,etc.The domestic research on the growth of diamond,the generation of color center and the theoretical calculation of related properties are also been carried out widely.General results show that,for the three-dimensional bulk materials,it can be effectively fabricated into advanced electronic devices since their defect states are effectively isolated from unnecessary disturbance so as to generate the quantum states of the defects or complexes which can be manipulated by external light or electromagnetic field,whereas for the two-dimensional single-layer materials,the present study frequently focused on its surface modification and improvement of applied performance.In this paper,we mainly use theoretical calculation method to study the spin manipulation of single defect state and the catalytic activity towards surface atoms of monolayer system.By theoretical simulation,we can find a way to explore design new functional materials.Some results has been summed as follow:?1?Based on the spin polarized density functional theory,we calculated the electronic structure of a new semiconductor ?-Si3N4,and introduced the VsiON defect center?composed of tetrahedral silicon vacancy combined with oxygen impurity,abbreviated as OV?as a single defect.Specifically,the change of electronic structure and the formation of energy under different charge states are analyzed and discussed.The calculated results show that:Firstly,similar to the center of negative-monovalent NV^-1 defect in diamond,that negative-monovalent charged defect center of y-Si3N4 is stable in the p-type ?-Si3N4 material.Secondly,OV^-1 defect center possess a paramagnetic ground triplet state with a net spin S=1.However,the photoexcited energy of the spin-conserved transition almost reaches to the infrared level,which is lower energetic excitation compared with that of diamond NV^-1.Then,based on the theoretical model of mean field approximation developed by our group previously,we have estimated the spin coherence time of the OV^-1 defect center,which is 0.4s at OK,and basically meet some requirements for the solid-state qubit candidates.Therefore,a series of theoretical calculations indicate that the OV^-1 defect center possess similar characteristics as the NV^-1 defect center of diamond,and ?-Si3N4 can also be considered as candidate material for quantum bit.?2?By first-principles calculation,we successfully optimized the simulated bent structure of the MoS2 monolayer.It is found that the hydrogen adsorption free energy of the material cannot be controlled to be close to zero merely through bending the Mo lattice layer.For the purpose of further improving its performance of hydrogen evolution reaction?HER?,we then introduce substituted N and O dopant into the bent part of MoS2 surface,which is equivalent to re-establish the electron cloud distribution around the active region of hydrogen adsorption.The combination of lattice bending and chemical doping is able to balance the two steps of HER:hydrogen adsorption and desorption.The calculated results show that the surface atomic site in the vicinity of the nitrogen dopant in N-doped bent-MoS2 monolayer is able to possess high performance HER activity comparable to that of the metal platinum catalyst.The idea of theoretically designing a monolayer material with high catalytic hydrogen evolution can be applied to the theoretical simulation and design towards other low-dimensional materials.?3?The third part is an extensional chapter.We will mainly introduce my theoretical work combined with experimental study directed by the group of Professor Chen Mingwei,Tohoku University in Japan.Similar to the second part of this article,which described the design of hydrogen evolution reaction catalyst,the catalytic performance of nanoporous graphene was gradually optimized to be infinitely close to the performance of metal platinum.The combination of three methods:the surface bending,the introduction of topological defects and the doping decoration significantly improve the catalytic activity of graphene.Specifically,the calculated results show that the existence of topological defects is able to further alter the charge distribution locally,and the enhanced electron cloud distribution gradient is the key to enhance the rapid transfer of electrons around catalytically active region.