Spatially resolved photoluminescence of laterally overgrown GaN

Abstract

The epitaxial lateral overgrowth (ELOG) of GaN has recently proven to be a suitable technique to significantly reduce the dislocation density in metalorganic vapor phase epitaxy (MOVPE) or hydride vapor phase epitaxy (HVPE) of GaN. We have investigated by spatially resolved photoluminescence on GaN overgrown from hexagonal openings and partially coalesced pyramids obtained by MOVPE. Different positions of the overgrowth were analyzed, i.e., the edge of the coalesced pyramid, the center, the starting pyramids and GaN underneath the dielectric. Whereas the photoluminescence (PL) spectra of starting pyramids and GaN underneath the dielectric behave about the same, a drastic difference between edge and center of coalesced pyramids is observed. Two PL bands are observed at 300 K, the band edge one, at 3.41 eV, and the yellow luminescence (YL) around 2.2 eV. The highest intensity of the 3.41 eV peak comes from the edge of the overgrowth, the lowest from the center. Conversely, the YL intensity is the strongest at the center of the overgrowth, once again by one order of magnitude. In addition, the YL could be resolved into overlapping gaussian lines, each of them corresponding to a given LO phonon replica. The lineshape is analyzed in the frame of configuration coordinate diagram, and the zero phonon line estimated to be at 2.53 eV.