Threading dislocations in molecular beam epitaxially grown films were studied using ultra-high vacuum ballistic electron emission microscopy in order to quantify fixed negative charges, at threading dislocations, with a spatial resolution of about 3nm and a local barrier resolution of about 0.01eV. In contrast to previous studies, no indication of fixed negative dislocation charge at specific threading dislocation structures was found; with a conservative upper limit of about 0.25 electrons per c-axis unit cell. Evidence of positive surface charge at threading dislocations and at step edges was found, and was tentatively attributed to local piezoelectric fields.

Characterization of Individual Threading Dislocations in GaN Using Ballistic Electron Emission Microscopy. H.J.Im, Y.Ding, J.P.Pelz, B.Heying, J.S.Speck: Physical Review Letters, 2001, 87[10], 106802 (4pp)