| GaN and BN in the group of Ⅲ-Ⅴ nitrides semiconductors possess very high luminous efficiency, hardness, thermal conductivity, radiation resistance. They are used in microelectronic devices, storage devices, blue green light-emitting devices and other photoelectric devices. As a kind of the most advanced semiconductor materials, they have aroused widely concern. GaN and BN have wurtzite and zinc blende crystals structures, in which the wurtzite structure has been extensively studied and applied at present.In this thesis the electronic band structure and phonon dispersion properties of the optimized wurtzite GaN and BN are studied, by choosing two different approximation methods, Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA), based on the density functional theory of the first principle method. The results indicate that the wurtzite GaN is direct band-gap semiconductor, but BN has the indirect band-gap. In the process of calculation, the GGA approximation is considered to be the Ga-3d electron orbital effect, and overestimates the energy of3d electronic state, LDA approximation research for s and p electronic states. The obtained GaN and BN band gaps by the two kinds of approximations are consistent well with other literatures. The contributions of different electron configurations to the electron energy levels can be clearly seen from the figures of density of states. The phonon dispersion curves for the wurtzite GaN and BN are obtained. The GaN and BN born effective charge tensors and high-frequency dielectric constants are also calculated by GaN and BN phonon spectra in the GGA approximation. Our results coincide very well with other theoretical and experimental works. Finally, the thermodynamic properties of the wurtzite GaN and BN are calculated by using the harmonic approximation method, and the phonon contribution free energy, internal energy, specific heat and entropy are obtained. |
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