Electron Holography Studies of the Charge on Dislocations in GaN

Off-axis electron holography in a transmission electron microscope is used to examine the charge on threading edge dislocations in $n-\mathrm{GaN}$ (0001). It is shown that the crystal inner potential is reduced within 10 nm of the dislocation consistent with a negatively charged core. The results can be explained by a simple unscreened potential due to a core charge of about $4\times {10}^7\mathrm{electrons}\mathrm{cm}{}^{-1\mathrm{}}$. The origin of this charge is discussed. The application of the method to other types of dislocation is also considered.