Electrical activity of dislocations in epitaxial ZnO- and GaN-layers analyzed by holography in a transmission electron microscope

Transmission electron microscopy was used to characterize dislocations in n-ZnO and n-GaN epitaxial layers grown on Al2O3(0 0 0 1) substrates. Threading segments of misfit dislocations with screw, edge and mixed character are observed with varying fractions depending on the epitaxial growth procedure. The electrical activity of single dislocations is studied by off-axis electron holography in a transmission electron microscope. An electrostatic potential in the vicinity of the dislocations is detected for ZnO and GaN, which clearly demonstrates that charges are present close to the dislocation core. Applying Read′s model for the potential of a screened line charge, high charge densities of approximately 2 elementary charges per nm dislocation length are derived.