Abstract
A computational approach to study the effect of threading edge dislocation density on photoluminescence in n-type wurtzite GaN is presented and the calculated results are compared with experimental data. A calculation domain with a dipole of edge dislocations in three-dimensional real space is analyzed and its size is varied to study the effect of dislocation density. A 6x6 k center dot p Hamiltonian is solved to determine the energy levels and wave functions for valence electrons using the finite element method; the conduction band is calculated separately by taking advantage of the wide band gap of 3.44 eV. The spontaneous emission spectrum is then evaluated. The electrostatic potential of the edge dislocation, due to its electron-acceptor nature, and the deformation potential associated with the strain field of the edge dislocation reduce the intensity and broaden the peak of the band edge emission. Besides the band edge peak, three distinct peaks are observed below the band edge transition energy. These peaks are from transitions to dislocation-localized hole states with energies within the band gap created by the electrostatic potential of the edge dislocations. Compared to the effect of the electrostatic potential, the strain field effect is negligible in generating emission peaks below the band edge transition energy, but it is still significant enough to contribute to broadening the band edge peak. The calculated band edge peak intensities closely agree with experimentally measured band edge photoluminescence intensities. The calculated and experimental data both show a significant reduction of band edge peak intensity for a dislocation density higher than 10(7) cm(-2) as the dislocation density increases. The intensity of band edge peaks reduces significantly with high dislocation densities and low carrier concentrations, which indicates that GaN becomes dislocation sensitive like other III-V materials if insufficient carriers are present.