The Research On The Electronic Structure Of YBaCuO-X High-T_c Superconductor And GaN/AIN Strained-Layer Superlattice

The electronic structures of halogen-doped Y-Ba-Cu-O high Tc superconductor and (GaN)n/(AlN)n Strained-Layer Superlattice (SLS) are calculated with recursion method in this paper. Recursion method, which is widely used, can calculate the density of states (DOS) without solving the Schrodinger equation, so it has the advantages of a relatively small amount of calculation and being able to solve non-periodic problems.The first part of this paper discusses the electronic structure of halogen-doped Y-Ba-Cu-O high Tc superconductors. The results show that Y and Ba atoms only donate their valence electrons and the DOS of Cu atoms are highly localized. The bonding situation is analyzed with the curves of the DOS. By comparing the Structure Energy, F prefers to occupy the vacant O(5) position or replace the oxygen atom at O(l) position. The difference of F, Cl and Br respectively replacing the oxygen atom at O(l) position is discussed. After the doping of halogen, the valences of Cu atom increase and those of O atom decrease, which means that the hole number of Cu increases and that of O decreases. From the Charge Transfer Model, we analyze the influence of halogen doping to the YBCO superconductor and discuss the reason for the improved superconducting properties. Our research can help understand the mechanism of halogen doping to YBaCuO superconductor and make a guide to the further experiment on this subject.The second part of this paper discusses the electronic structure of (GaN)n/(AlN)n strained-Layer Superlattice under free-standing conditions. The electronic DOS and atomic valences of GaN, A1N bulk material and the (GaN)n/(AlN)n Superlattice are obtained. The results show that the Eg of the SLS is as big as those of GaN and A1N. There exists mixed bonding among Ga(Al) and N atoms of the SLS. When there is a vacancy in the SLS, there will form defect energy level in the Eg. The situation of the SLS being doped with Mg and C atoms is also discussed. Finally we study the influence of the layer number(n) to the SLS and the surface state of the SLS. (GaN)n/(AlN)n Superlattice will be widely used in making the optic-electrical devices and our research can be of great help for the further theory and experiment research of (GaN)n/(AlN)n Superlattice.