Transmission electron microscopy (TEM) is used to determine the composition of quaternary (Ga,In)(N,As) quantum wells (QWs). Through a combined analysis of the chemically sensitive (002) dark-field (DF) images and the lattice-resolving high-resolution TEM images, the local distributions of nitrogen and indium in the growth direction are determined. In particular, we are able to directly detect the existence of indium segregation in (Ga,In)(N,As) QWs. A comparison with the indium distribution profile in the nitrogen-free (In,Ga)As QWs, grown under similar conditions, revealed that incorporating N into the alloy enhanced indium segregation
