Electron scattering due to threading edge dislocations in n-type wurtzite GaN

Abstract

The effect of electrically active VGa–ON threading edge dislocations on drift and Hall mobilities in n-type epitaxial wurtzite (WZ) GaN is investigated theoretically. The charge distribution along the dislocation core is first obtained by means of a density-functional theory atomistic calculation; the two N atoms near the missing Ga atom at the dislocation core are found to be electron acceptors. An accurate analytical expression for dislocation electrostatic strength is then derived for the case of up to −2q charge per structural unit of the threading dislocation core. This strength factor is determined by minimizing the total increase of free energy per site of the partially charged dislocation line. Two different models of scattering potentials for charged dislocation lines are then used to determine the dislocation effect on in-plane electron mobility, and closed-form solutions for the dislocation contribution to drift and Hall mobilities are derived for the more accurate potential. By estimating the effects of other scattering mechanisms, the total mobility is then compared with available experimental data. It is found that for free-carrier concentrations higher than 1016cm−3, reducing dislocation density below ndis=108cm−2 has little beneficial effect on total mobility for typical WZ GaN samples.