Advanced epitaxial techniques such as molecular beam epitaxy or metal-organic chemical vapour deposition have made it possible to grow interfaces between two semiconductors flat up to one atomic monolayer. The possibility of fabricating a heterostructure of strictly-defined parameters, a quasi-two-dimensional nature and sharp density of states, has stimulated both theoretical and experimental research and shortly found many applications including LEDs, lasers, high electron mobility transistors, IR photodetectors, etc. In this work a detailed study of optical properties of excitons in double...