First-Principles Studies Of Phonons And Thermal Properyies Of AIN And InN In Wurtzite Structure

Group-Ⅲ nitrides have attracted considerable attention during the past decade due to technological applications in optoelectronic and electronic devices. Aluminum nitride (AlN) and Indium nitrideis (InN) the important materials among them. It has high thermal conductivity, high melting point, and large bulk modulus. Attention has also been paid to the lattice vibrations (phonons), which related closely to their electric, optical as well as thermal properties.In this thesis, we calculate the band structure, density of states, phonon dispersions and thermodynamic properties of wurtzite AIN and InN using the local density approximation (LDA) and the generalized gradient approximation (GGA). The software PWscf of Quantum-Espresso is used. The results show that wurtzite AlN and InN are direct gap semiconductors. The phonon dispersion curves for the wurtzite AIN and BN are obtained. The AIN and InN born effective charge tensors and high-frequency dielectric constants are also calculated by AIN and InN phonon dispersions in the LDA and GGA approximation. The phonon internal energy, vibrational free energy, specific heat and entropy of AlN and InN as functions of temperature are obtained. The calculated values are in agreement with available experimental data.