Application of Kelvin Probe Microscopy for Nitride Heterostructures

Kelvin probe microscopy is an experimental technique designed to investigate fluctuations of surface potential (work function per electron) related to distribution of electric charge or variations in composition. The paper describes principle and precision of measurements. The results obtained for group-III nitrides semiconductor heterostructures grown on c-plane sapphire by metal-organic vapour phase epitaxy are presented. The observations concerns defects: inversion domains for Ga- and N-polar layers, threading dislocations and effects of spontaneous polarization leading to 2D carrier gas. To achieve insight in the evolution of defects, bevelled and cross-sectioned samples were investigated along with surface of "as grown" layers. Applicability of standard Kelvin probe microscopy method was also extended by investigating dependence of the surface potential on variable wavelength illumination, offering opportunity for spectroscopy of individual defects.