Dislocation reduction in GaN epilayers by maskless Pendeo-epitaxy process

Facet structures of GaN grown by the Pendeo-epitaxy (PE) process with low-pressure metalorganic chemical vapor deposition (LP-MOCVD) are controlled by growth temperature. PE growth without the use of a mask, termed 'maskless' PE, was performed to reduce crystallographic tilt and to eliminate a source of impurities in the overgrowth material. Tilting behavior and crystalline properties, which were investigated from the result of (0002) X-ray diffraction rocking curves taken perpendicular and parallel to the seed stripe direction, can be improved with high growth temperature. The propagation mechanism of the threading dislocations in the different GaN facet structures is investigated by transmission electron microscopy (TEM). Two-step growth in the PE process is proposed; in this technique, bending of threading dislocations due to facet structure is observed. The two-step growth process shows much lower dislocation density and better crystal quality than conventional maskless PE GaN.