First Principle Calculation Of Gallium Nitride Using Quantum Espresso Package

Abstract

Gallium Nitride is a wide band gap semiconductor belonging to group III-V. It is commonly used in light emitting diodes (LED) and many optoelectronic devices fabrications. However its electronic and structural properties are not well studied using density functional theory. In this thesis, the first principle calculation based on density functional theory (DFT) was employed to investigate the electronic and structural properties of hexagonal wurtzite Gallium Nitride using quantum ESPRESSO package. A number of convergence test were performed to establish the optimal value of various parameters in the numerical calculations. Firstly, the total minimum energy of gallium nitride per atom was calculated as a function of cutoff energy and k-points sampling. Secondly, the optimal lattice constants of bulk GaN was calculated for a series possible parameters using the results obtained from energy convergence test (i.e 80 Ry and 10 × 10 × 10 k-points). Moreover the band structure and density of states of GaN have been calculated based on the frame work of density functional theory. The results of calculations show that the total minimum energy of GaN per atom is monotonically decreasing with increasing cutoff energy due to variational principle. However, this trend can not be predicted from increasing the k-point sampling. The computational value of the equilibrium lattice constant was ( a = 4.16 and c = 6.65) Angestrom. The obtained result was overestimated as compared to the experimental result. The calculated band structure and density of states of GaN was 3.1 eV and 3.0 eV respectively, which was in a good agreement with experimental value (3.4 eV).