Single wavelength ellipsometry with high time resolution was used for in situ control of MCT structures growth. Potential barriers and wells were grown with ellipsometric control of composition and thickness. Accuracy of barrier (well) thickness determination depends on the absolute value of the thickness and typically amounts to 0.1 nm. For MCT layers with continuously varying composition a simple interpretation of ellipsometric data was suggested allowing a control over composition profile in real time. Using this approach, MCT structures were grown with a top gradient barrier layer, preventing carriers surface recombination. (C) 2003 Elsevier B.V. All rights reserved.