First-Principles Study Of The Structural And Electronic Properties For ZnO Series And GaN Based Diluted Magnetic Semiconductors

In this thesis,using a pseudopotential plane-wave method based on Density-Functional Theory(DFT),we mainly investigated three things below.The first thing is the structural transition of ZnO under lower pressures.In this work, we used the energy state of equation and elastic modulue calculations to clarify the work. In the energy state of equation subsection,we also considered the structural transition of ZnS under lower pressures.The results show that at about P=12.4 GPa and P=17.85 GPa,B4 ZnO translates to B1 ZnO and B3 ZnS translates to B1 ZnS,which agree well with available results.Moreover,at the early stage of the structural transition from B4 ZnO to Bl ZnO,the lattice parameter ofαdecreases with c/a increasing and u reducing.The second thing is the studies of the electronic and optical properties of ZnO and related materials,which including Zn_4-yX_yM(y=0 or 1;M=N,Sb,Cl or I),the spinels ZnAl₂O₄,MgAl₂O₄ and their related oxides.About the Zn_4-yX_yM(y=0 or 1;M=N, Sb,Cl or I),studies show that Zn d-X p orbital interaction plays an important role in determining the p-type conductive possibility.Reducing Zn d-X p orbital interaction leads to the increasing of the p-type conductive tendency.The analysis of the optical spectra indicates that with the atomic number of X increasing,the main peaks of the op-tical spectra shift to lower energy region.Furthermore,different carrier doped compounds exhibit different characteristics.The spectra of p-(n-)type doped systems are similar to that of the corresponding undoped natural n-(p-)type materials,but different from the spectra of the corresponding undoped natural p-(n-)type pure ones.About the spinels ZnAl₂O₄,MgAl₂O₄ and their related oxides,both the electronic structures and the optical properties of MAl₂O₄ are different from those of MO and Al₂O₃(M=Zn,Mg) due to the atomic rearrangement.Therefore,the optical properties of MO and Al₂O₃ (M=Zn,Mg)should not be regarded as references of those of MAl₂O₄.The third thing is the studies of electronic structures and magnetic properties of Ga_1-xMN_x(X=0.5,0.125,0.037;M=Ti,V,Cr,Mn,Fe,Co).In this work,we mainly dicussed the magnetic moment changes of various 3d transition metals with different solubilities in GaN,and the effect of the transition metals on their neighbors.The results show that the atomic outnost electronic states of the transition metals take a decision role to the value of their magnetic moments in doped states.Moreover,the positions of the doped energy levels also change with the changing of the doped elements.Among the studied transition metals,the magnetic moment of Mn ion in its doped states is the biggest.But Cr doped system has the biggest reasonable solubility.The results also show that the effects of solubilities to the transition metals themselves are not big,but big to their neighbors.To the nearest neighbors of the doped transition metals,the changing of solubilities of the transition metals will change not only the value of their polarization magnetic moments but also their polarization directions.If only considering the reasonable solubilities,Cr is the best doped element in GaN based DMS among the studied doped elements.But if changing the consideration reason from the transitional metals to the neareast neighbors of them,doped Fe or Co is better.