Angular distribution of molecular beams and homogeneous layer growth: optimization of geometrical parameters in molecular beam epitaxy

Preceding studies of angular distribution flows issued from molecular beam sources used in molecular beam epitaxy are analysed by comparison with anal ogous studies as performed on the Knudsen effusion cell method. A new archi tecture of the effusion sources and substrate relative disposition for epit axial growth is proposed which discards any re-vaporized parasitic flow of molecules and which is aimed to warranty reproducible and reliable impingin g flows. Impinging molecular flows on substrates are then calculated for th e two usual device symmetries-cylindrical and spherical, and in case of fix ed or rotating substrates. Two minima for thickness or composition gradient s are found for rotating substrates that correspond to an angle between the substrate normal axis and the sources-substrate axis equal to 35.26 degree s for cylindrical symmetry and to 45 degrees for spherical symmetry, whatev er be the source substrate distance and relative radii. Advantages of this new architecture are underlined. (C) 2001 Elsevier Science Ltd. All rights reserved.