Investigation Of The Valence Structure And Modulation Of Algan And AlGaN Low-dimensional Structure

The luminescence process of Class ? nitride semiconductors is mainly determined by the energy band structure at the Gamma Point?k=0?.Because the Al_xGa_1-x N of the fiber-zinc mine is a kind of s-orbit,which has complete symmetry,the valence band structure of Al_xGa_1-x N in the wurtzite is mainly formed on the p orbital,which plays a leading role in the direction of light.In this thesis,the density functional theory of the first principle is used to calculate the microscopic properties which cannot be realized by macroscopic experiments,and the photoelectric properties of ideal Ga N and the optical polarization characteristics of Al_xGa_1-x N lattice structure under different Al components are calculated and analyzed:1.Based on the material model of Ga N and Al_xGa_1-x N?x=0.2,0.4,0.6,0.8,1?materials established by the Material Studio software,the VASP software package of first principle was used to calculate and study the energy band offset,total state density,partial state density and optical properties of the Al_xGa_1-x N material relative to Ga N.The calculatedresults show that the band offset of the conduction band increases with the increase of the aluminum component,which is quite different from the negligible band offset of the valence band.The change of aluminum composition makes the material have different effect on the light efficiency of ultraviolet light of the same wavelength.2.The influence of the lattice structure change of Al_xGa_1-x N?x=0.2,0.4,0.6,0.8,1?on the valence band,luminous polarization and optical properties was compared and analyzed.For the Al_xGa_1-x N material of the same aluminum group,the lattice structure change leads to the higher light ratio of the CH band in the Al_xGa_1-x N material.For the Al_xGa_1-x N materials of different aluminum component,the CH band luminescence ratio in the Al_xGa_1-x N material of high aluminum composition is larger than that in the Al_xGa_1-x N material of the lower aluminum component.The change of lattice structure in the Al_xGa_1-x N material of high Al composition?x>0.6?makes the refractive index,absorption coefficient and reflectivity of 200-400 nm wavelength light decrease.3.The valence band structure and optical properties of the step-shaped Al_0.69Ga_0.31 N,Al_0.63Ga_0.37N/ Al0.75Ga0.25 N and Al0.75Ga0.25N/Al_0.63Ga_0.37 N Quantum well structures are calculated and analyzed.From the calculation results,the polarized light produced by the three kinds of step-shaped quantum well structures is gradually enhanced,and the positive rays are gradually reduced.Al_0.69Ga_0.31 N and Al0.75Ga0.25N/Al_0.63Ga_0.37 N are similar in all basic optical properties,Al_0.63Ga_0.37N/Al0.75Ga0.25 N the basic optical properties are relatively different from the previous two.