Threading dislocations in variously doped single layers, grown by metal-organic vapor phase epitaxy onto (00•1) sapphire, were investigated by means of tapping-mode atomic force microscopy and scanning surface potential microscopy. In Mg-doped, and in some undoped GaN layers, surface potential variations of about 0.1V (due to additional negative Coulomb charges) appeared around the dislocation/surface intersections. In Si-doped, and in some other undoped layers, the surface pits were electrically neutral; with no systematic surface potential signal. These differences in charge state were attributed to decoration of the dislocation core with other defects.

Electrical Microcharacterization of Dislocation-Related Charges in GaN-Based Single Layers by Scanning Probe Microscopy Techniques. A.Krtschil, A.Dadgar, A.Krost: Journal of Crystal Growth, 2003, 248, 542-7