The Research Of Doped ZnO And In₂O₃ By First-principles

The rapid development of science and technology makes people more and more critical of the requirement of semiconductor materials. How to meet the needs of modern people for semiconductor materials and how to improve the properties of semiconductor materials to expand its applications is a very worthy research field. Among metal oxide semiconductor materials, In2O3 is a representative of the second generation of semiconductor materials, while ZnO is a representative of the third generation of semiconductor materials. They have been widely used for optoelectronic devices and new energy field. However, problems of limited properties have become an issue to expand its application field. Recent research shows that the electronic and optical properties of the materials can be improved by doping metal and nonmetal in materials. Coupled with existing optical and electrical properties of the In2O3, the addition of controllable magnetism could make a technologically essential material, where both charge and spin of electrons can be manipulated simultaneously. In the present article, we present the respectively studies of the influence of oxygen defect in ZnO structure on the electro-optical properties; and the introduce and tunable ferromagnetic coupling by doping Mo element into In2O3 lattice structure.This article mainly includes the following concerned research:Firstly, How different layer of oxygen defect affects the surface of zinc oxide structure; Secondly, How different layer of oxygen defect affects the electron structure on the surface of the zinc oxide; Finally, what is the source of magnetic in Mo doping In2O3 system, how the magnetic coupled between the Mo atoms inside the system and what the influence of intrinsic defects like oxygen vacancy on the magnetism is. All the studies are based on the theoretical calculations which are performed on the Cambridge serial total energy package (CASTEP) code, which is based on ultrasoft pseudopotentials method.The main results obtained from the present studies are summarized as follows:1. This article studied the influence of oxygen defect on the structure and electronic structure of ZnO system. First, the impact of intrinsic oxygen defect on the architecture was studied. It is found from the comparative analysis of the surface of ZnO, with oxygen defect and complete lattice structure respectively, that the oxygen vacancy has significant effect on the structure of atom nearby, while there is little effect on the atom far away.2. We studied the intrinsic oxygen defects on electronic structure of the system. The results show that due to the intrinsic defects of oxygen, excess free electrons which the zinc atom provided to oxygen would alter the electronic structure of ZnO. By a comparative analysis of the surface of ZnO, with oxygen defect and complete lattice structure, we found a gradually 0-6eV move of electrons towards low energy in conduction band; and a-5-0eV move of electron in the direction of low energy in valence band. Because oxygen defects in ZnO lattice structure have less influence on the electronic structure and optical properties in the high energy region, it is believed that the existence of oxygen defects just adjusts the optical absorption of system in low energy.3. It is shown that the Mo substitution creates the spin splitting impurity states in the bottom of conduction band, therefore, Mo doping in In2O3 transfers it to an n-type semiconductor.4. The MoIn induces magnetic moment of 1.752 μB for b-site (or 1.259 μB for d-site) which mainly comes from the partially filled d-orbital of Mo atom and its hybrid with the p-orbitals of six neighboring 0 atoms. So, the Mo-doped In2O3 becomes a n-type half-metallic magnetic semiconductor.5. Oxygen vacancy Vo, as an electron donor provides two electrons to the MoIn. Because of lacking the attraction from atomic nucleus, these compensating electrons tend to disperse in space and interact with the adjacent metal ions. The calculation results show that the compensating electrons will prefer to localize near the Mo sites. This will facilitate the formation of magnetism. We could propose that related defect complex is the main source of the observed FM in the Mo-doped In2O3.