Analysis of crystal defects on GaN-based semiconductors with advanced scanning probe microscope techniques

• We prepared operating GaN light-emitting diode test structures on sapphire substrates.
• These structures were analyzed by advanced scanning probe microscopy techniques.
• The current mapping shows the correlation of surface pits and current spots.
• About 50% of the surface pits coincide to current spots.
• Local current–voltage characteristic on surface pits reveal enhanced conduction.

The correlation of surface pits with leakage currents in gallium nitride (GaN) films are studied with scanning probe microscopy (SPM) techniques. The analyses were performed at both single n-GaN films grown on free-standing GaN and completely processed GaN light-emitting diode (LED) structures on sapphire substrates both grown by metal organic chemical vapor phase epitaxy. Topographical SPM images acquired with ultra-sharp probes were superimposed with current maps obtained by conductive atomic force microscopy (CAFM). The applicability of two different modifications of CAFM techniques has been studied. For both sample types, CAFM has revealed a clear correlation between forward-bias leakage current and locations of surface pits. In case of the LED structure, additional local current–voltage characteristics show that enhanced current conduction occurs in both forward and reverse bias on surface pit positions.