Investigation of the charge on threading edge dislocations in GaN by electron holography

We present direct evidence for the charging around end-on threading edge dislocations in n-type GaN doped with silicon by off-axis electron holography in a transmission electron microscope. It is shown that the inner potential is reduced by up to 2.5 V within 10 nm of the dislocation, consistent with a negatively charged core. The results, which can be fitted with an unscreened potential, are consistent with a line charge of about 2 electrons/ c, where c = 0.52 nm is the unit cell parameter of GaN. The origin of this line charge is discussed. The application of the method to other types of dislocation is also considered.