The characteristics of dislocation-related leakage current paths in an AlGaN/GaN heterostructure grown by molecular-beam epitaxy, and their changes due to local surface modifications, were investigated by using conductive atomic force microscopy. When a voltage was applied between the tip of an atomic force microscope and the sample, a thin insulating layer was formed in the vicinity of the leakage paths where current was observed. As the insulating layer reached a thickness of 2 to 3nm, the leakage current was blocked and subsequent growth of the layer was prevented. Although conductive screw or mixed dislocations were observed, dislocations with a screw component that did not conduct current were also noted. The reverse-bias leakage current was reduced by a factor of 2 in a large-area diode, fabricated on an area modified in this manner using an atomic force microscope, as compared with typical diodes fabricated on unmodified areas having a comparable series resistance. This confirmed that dislocation-related leakage current paths were a major component of the reverse-bias leakage current in Schottky diodes, fabricated on nitrides.

Reduction of Reverse-Bias Leakage Current in Schottky Diodes on GaN Grown by Molecular-Beam Epitaxy using Surface Modification with an Atomic Force Microscope. E.J.Miller, D.M.Schaadt, E.T.Yu, C.Poblenz, C.Elsass, J.S.Speck: Journal of Applied Physics, 2002, 91[12], 9821-6