Effect of screw dislocation density on optical properties in n-type wurtzite GaN

摘要

The effect of open-core screw dislocations on photoluminescence in n-doped wurtzite GaN epilayer is studied computationally and compared with experimental data. A k(centre dot)p Hamiltonian calculation domain is set up to contain a dipole of open-core screw dislocations, and its size is varied according to the desired dislocation density. Using the finite element method, energy levels and wave functions for conduction and valence states are determined in three-dimensional real space; the emission spectrum is then evaluated. The void associated with the dislocation core and the deformation potential due to the strain surrounding the core perturb the density of states and reduce the photoluminescence (PL) spectrum intensity accordingly. For dislocation densities below a transition density of around 10~(8) cm~(-2), the deformation potential effect dominates in reducing the PL intensity; above this dislocation density the effect of the missing material at the core dominates. The calculated photoluminescence results agree with experimental near-band edge PL intensity data well. Both the experimental and calculated PL spectra indicate a significant reduction in the optical response for a dislocation density larger than 10~(7) cm~(-2).