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Buffer layers in semiconductors

Design rules are being developed for the controlled growth of buffer layers on gallium arsenic, indium phosphorus aand silicon substrates. Buffer layers should provide the selected lattice parameter and a defect density no greater than normally available in conventional substrates.

Buffer layer relaxation has been studied for indium gallium arsenic on gallium arsenic for a range of indium content up to 50%. All layers follow the same strain relaxation behaviour, following an empirical curve with a threshold then a steady reduction in residual strain. This appears to hold for material grown by molecular beam epitaxy (MBE), atomic layer molecular beam epitaxy (ALMBE) and chemical beam epitaxy (CBE), as long as 2-dimensional growth conditions can be maintained. Layers under tensile strain may crack and do not follow the empirical curve even after annealing. Considerable progress has been made by the consortium in the rational design of multilayers involving strain steps with and without tensile components such that relaxation occurs at predictable interfaces. The fundamental basis of the empirical curve is being investigated.

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