Electron microscopy was used to characterize metalorganic chemical vapor deposited multiple quantum well structures which underwent a so-called blue shift in luminescence during thermal processing. The sample exhibited a shift, towards shorter wavelengths, of more than 100nm during annealing at 750C. The structural modifications which led to the blue shift included the elimination of atomic ordering in the quaternary barrier layers of the material, plus appreciable layer interdiffusion. A method was described by which quantitative analyses of the layer composition and lattice parameter could be obtained, at a spatial resolution of better than 2nm, by making energy-dispersive X-ray microanalyses in a scanning transmission electron microscope. Such analyses showed that interdiffusion occurred along a non-linear (non lattice-matched) path, where the group-V diffusivities exceeded those of group-III elements. This resulted in the incorporation of excess coherency strains, of up to 0.5%, in the quantum-well regions.

R.E.Mallard, N.J.Long, E.J.Thrush, K.Scarrott, A.G.Norman, G.R.Booker: Journal of Applied Physics, 1993, 73[9], 4297-304