A direct correlation between the structural and luminescence properties of thick InxGa1-xN layers has been achieved on a microscopic scale using highly spatially resolved cathodoluminescence. Surface roughening is typically observed in growth by metalorganic vapor phase epitaxy of thick InxGa1-xN layers for x≥0.1. Although the film remains highly planar, craters and protrusions appear on the surface. These surface defects are associated with redshifted luminescence indicative of indium segregation, and are related to threading dislocations in the films. © 2002 American Institute of Physics.