An Investigation of III-N type semiconductors' lattice dynamics using the adiabatic bond charge model

SUMMARY An Investigation of III-N Type Semiconductors' Lattice Dynamics Adiabatic Bond Charge Model Keywords: III-N nitrides, bond charge, lattice dynamics, short range interactions, coulomb interaction, bond charge model Group-Ill nitrides hold a special place among materials, mainly due to their desirable optoelectronic and thermal properties. These materials crystalline in cubic zinc-blende as well as hexagonal wurtzide phases. A thorough understanding of lattice dynamics of both phases is of importance both at the fundamental level as well as in determining thermal and electronic properties of these materials. In this work, we have studied the lattice dynamics of zinc-blende phases of GaN, A1N, BN and InN using the adiabatic bond charge model. The theories of the Born- Von Karman model, the valance force model, the shell model and rigit ion model are explained. We then study lattice dynamics of group III nitrides using the adiabatic bond-charge model. The adiabatic bond charge model is mainly based on the bond- charge model of Phillips an Martin. According to this model the BCs are allowed to move adiabatically, whereas in the bond-charge in the model of Phillips and Martin they always located midway between the two ions for homopolar semiconductors. In zincblende material groups the BC is shifted towards the more electronegative species. The adiabatic bond charge model proposed by Weber [17] is considered to be physically appealing that computationally much less demanding. In this study, for the the lattice dynamics of group-Ill nitrides three types of interactions are considered; Coulomb interaction between particles (ion-ion, ion-bc and bc-bc), short-range interactions (ion-ion, ion-bc, bc-bc) and non-central (or bond bending) interaction of Keating type between bond charges, as well as between ions and bond charges. In the last chapters the phonon spectra, density of states and vibrational vector for nitrides have been given.