Surface morphology and electronic properties of dislocations in AlGaN/GaN heterostructures

Scanning force microscopy was used to examine the surfaces of AlGaN/GaN het erostructures grown by molecular beam epitaxy (MBE) on GaN templates prepar ed by hydride vapor phase epitaxy (HVPE) Away from dislocations, the MBE gr owth replicates the surface morphology of the HVPE film, with monolayer ste ps clearly visible in topographic images. However, the surface morphology n ear dislocations depends strongly on the MBE growth conditions. Under Ga ri ch growth the dislocations appear as hillocks, while under stoichiometric g rowth they appear as pits. A dependence on Al concentration is also observe d. Surface contact potential variation near dislocations is consistent with excess negative charges surrounding by a depletion region, but this was ob served only for the film grown under stoichiometric conditions.