| Quantum mechanical computational techniques are used to study material properties for technologically interesting semiconductors and their alloys from first principles. The approach is based on density functional theory and the calculations are performed using the full-potential linear muffin-tin orbital methods.; This dissertation consists of three main parts: (1) A study of the elastic and related phonon properties of binary III-nitrides. (2) A study of the 'fine structure' of the band structure at the band edges and its dependence on strain, (3) A study of the miscibility and bandgap bowing in III-N alloys. In all three problems, attention is paid in the relations between corresponding properties in wurtzite and zincblende structures.; The study of the elastic constants for BN, AlN, GaN, and InN shows good agreement with experimental data, some of which became available only after our calculation were finished. Martin's transformation method deriving wurtzite elastic constants from those of zincblende is found to be accurate. We determine the bond-stretching and bond-bending parameters, {dollar}alpha{dollar} and {dollar}beta{dollar}, of Keating model. A systematic study of the full phonon spectrum at {dollar}Gamma{dollar} is made for wurtzite GaN and InN and is used to interpret recent Raman data on InN.; In the second part, we investigate the detailed nature of the band structure art the band edges. We determine the effective mass tensors and the related Rashba-Sheka-Pikus and Kohn-Luttinger Hamiltonian parameters for wurtzite and zincblende GaN and AlN.; The shift and splittings of the energy bands due to strains are used to obtain the deformation potentials for the zincblende crystals at symmetry points and for the band edge states of the wurtzite.; Finally, we study group III nitride alloy system involving AlN, GaN, and InN. The cluster expansion approach is used to obtain the behavior for the disordered alloys using the electronic structure of ordered compounds. The important effects of bond length and volume variation on electronic properties are taken into account. Band gaps of pseudo-binary alloys are obtained. An interpolation formula for the gap of the full pseudo-ternary Al{dollar}sb{lcub}x{rcub}{dollar}Ga{dollar}sb{lcub}y{rcub}{dollar}In{dollar}sb{lcub}1-x-y{rcub}{dollar}N system is proposed and tested. Extension of the results to the wurtzite alloys is discussed. |
