Scanning capacitance microscopy studies of unintentional doping in epitaxial lateral overgrowth GaN

Abstract

Four samples were grown by epitaxial lateral overgrowth (ELOG) using different magnesium precursor fluxes during the coalescence stage. These samples were studied in cross section using scanning capacitance microscopy and scanning electron microscopy. The resulting images revealed the existence of several differently doped regions in the ELOG structures including n-type doping in the GaN initially grown through the ELOG mask’s windows, and undoped GaN after coalescence had been completed. In addition, samples for which a magnesium precursor flux had been present during the coalescence of the GaN stripes also exhibited p-type doping. From an analysis of the spatial distribution of the unintentional doping in the ELOG material, it has been possible to propose that the incorporation of the n-type dopant was slower on the (0001) facet than the {112¯2} facets. This facet dependent difference in incorporation rates also helps to explain the nonuniformity in thickness of n-type conductive layers seen at the GaN/sapphire interface when a three-dimensional growth mode is employed in the early stages of growth.