Characterization of individual threading dislocations in GaN using ballistic electron emission microscopy

Threading dislocations (TDs) of molecular beam epitaxy grown GaN film were studied with ultrahigh vacuum ballistic electron emission microscopy in order to quantify any fixed negative charge at identifiable TDs, with approximately 3 nm spatial and approximately 10 meV local barrier resolution. In contrast to several prior studies, we find no indication of fixed negative dislocation charge at specific TD structures, with a conservative upper limit of approximately 0.25 e(-) per c-axis unit cell. We do observe evidence of positive surface charge at TDs and at GaN step edges, which may be due to local piezoelectric fields.