Investigation of properties of In-related alloys by AFM

MOCVD grown Al1-xInxN/AlN/GaN and InxGa1-xN/GaN heterostructures have been characterized by Atomic Force Microscopy in semi-contact and conductive mode. In-related alloys consist of grain-like structures indicating step flow and 3D-growth with threading dislocations (TDs) of density equal to ~108/cm2, the origin of which is mostly attributed to lattice mismatch between GaN and sapphire. These TDs with screw or mixed components terminate at the surface of overgrown layers as V-defects, which are six-facetted inverted pyramidal structures. Strain relaxation mechanism, formation of cracks and its propagation to the surface of the samples were also investigated. With phase-imaging (in semi-contact AFM), we have traced sites of indium segregation in the V-defects, surface-relaxation and crack propagation in In-related alloys. These sites in V-defects and cracks were found to be highly conductive by current-AFM either due to the presence of In-segregation or due to lowering of potential barrier as a consequence of strain-relaxation. They may be the possible dominant cause of leakage current in Schottky diodes. Further, current-voltage characteristics were obtained using AFM tip and barrier lowering due to image charges or trapped charges at the interface could be the conduction mechanism present in these structures. This has allowed us to calculate the local 2DEG density. This work was supported by the EU under Project No. PITN-GA-2008 213238_RAINBOW