Multistep method for threading dislocation density reduction in MOCVD grown GaN epilayers

A new multistep MOCVD method for growing GaN is used to suppress threading dislocations in GaN epilayers on c-plane sapphire. A nucleation island density of as low as 2.5 × 10 7 cm -2 is reported. Developed subsequent overgrowth prevents the formation of new islands and stimulates the inclination of threading dislocations inside nucleation islands before their coalescence. GaN epilayers with a threading dis location density of 5.0 × 10 7 cm -2 are grown by the method. Nucleation island morphology and threading dislocation density are analyzed by atomic force microscopy. Transmission electron microscopy is used to support the results for the threading dislocation density and to evaluate the epitaxial relationship of the GaN films. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.