AFM and CAFM studies of ELO GaN films

Abstract

The techniques of atomic force microscopy (AFM) and conductive AFM (CAFM) have been used to study the morphology and conduction properties of <i>a</i>-plane GaN films grown via epitaxial lateral overgrowth (ELO). Four GaN samples were prepared using metal organic chemical vapor deposition (MOCVD) with slightly different growth conditions. In AFM images, the coalesced ELO films show undulations, where the window regions appear as depressions with a higher defect density than surrounding areas. At reverse bias above 20 V, lower quality samples show localized leakage defect sites inside the window regions, whereas higher quality samples show no localized leakage. This behavior is consistent with previous observations on non-ELO samples where significantly enhanced localized leakage occurs at voltages above 15 V. Surface oxidation was also observed, where continuous scanning at reverse bias results in decreased conduction. This CAFM study confirms that ELO-grown GaN samples show enhanced reverse-bias leakage inside window regions where a higher defect density is present.