Electrical conduction along edge dislocations in GaN (Vol. 44 No. 2)

Electrical conduction along dislocations in semiconductors has attracted much attention both from fundamental and practical viewpoints. Fundamentally, such dislocations can be one-dimensional electronic systems and their conduction mechanism has already been investigated. On the other hand, the issue of the dislocation conduction should be practically important because it might degrade the performance of semiconductor devices. Here, local current conduction due to dislocations in GaN has been studied by scanning spreading resistance microscopy (SSRM). Fresh dislocations, induced by plastic deformation, were used to see their intrinsic properties.

The SSRM images showed many bright spots with high conductivity. The spots form chains along the slip direction and appear to be due to the edge dislocations introduced by deformation, which are terminated at the observed surface. Here, the line direction and Burgers vector of the dislocations are l = [0001] and b = (a/3) [1 10], resp. Previous studies have shown that grown-in screw dislocations with l = b = c[0001] are conductive but that grown-in edge dislocations with l = [0001] and b = (a/3) [1 10] are not, in contrast to our results. This apparent discrepancy should arise from the difference in the core structure between deformation-induced fresh dislocations and grown-in dislocations possibly decorated with native point defect or impurities. Theoretically, the electronic structures of the dislocations in GaN have been shown to change sensitively with the core structure, which should bring large conductivity differences. Local current-voltage spectra, measured at conductive spot positions, indicated a Frenkel-Poole mechanism for the conduction. These findings provide new insights into the issue of electrical conduction along dislocations in semiconductors.