  The strain state and composition of a 400 nm thick (In,Ga)N layer grown by
metal-organic chemical vapor deposition on a GaN template are investigated by
spatially integrated x-ray diffraction and cathodoluminescence (CL)
spectroscopy as well as by spatially resolved CL and energy dispersive x-ray
analysis. The CL investigations confirm a process of strain relaxation
accompanied by an increasing indium content toward the surface of the (In,Ga)N
layer, which is known as the compositional pulling effect. Moreover, we
identify the strained bottom, unstrained top, and gradually relaxed
intermediate region of the (In,Ga)N layer. In addition to an increase of the
indium content along the growth direction, the strain relaxation leads to an
enhancement of the lateral variations of the indium distribution toward the
surface.
