The compositional profiles in ultra-microtomed cross-sectional samples of epilayers of Hg1-xCdxTe and superlattices which had been grown via metalorganic chemical vapor deposition, were measured at the 10nm scale by using analytical electron microscopy. The results compared well with the predictions of a numerical model for interdiffusion which made use of published analytical expressions for the diffusion coefficient. The absorption contrast in electron micrographs revealed changes, in the apparent layer thickness, that were in excellent agreement with the theoretical model. Computer simulations of the interdiffused composition profiles (in which the temperature, deposition rate, and thickness of each individual layer was specified), together with the annealing conditions and the cooling rate to room temperature, successfully modelled the interdiffused composition across various (Cd,Hg)Te superlattice boundaries. It was demonstrated that 3 published expressions for the interdiffusion coefficient yielded essentially indistinguishable composition profiles when the growth temperature was treated as an adjustable parameter, and was optimized so as to give the best fit between experiment and theory. The analytical formulae for the diffusion coefficients were extrapolated to temperatures below their stated range of applicability. Limited reactor temperature profiling indicated that the Ludington expression gave the best absolute temperature dependence. Post-growth cooling was responsible for only a small fraction of the interdiffusion which, in most cases, was negligible.

C.J.Rossouw, G.N.Pain, S.R.Glanvill, D.C.McDonald: Journal of Crystal Growth, 1990, 106[4], 673-82