Smooth and coherent layers of GaAs and AlAs grown by molecular beam epitaxy

Periodic ultrathin layers of GaAs and AlAs with a few periods have been grown by molecular beam epitaxy under computer control. For such structures, x-ray scattering measurements at small angles show a series of principal and secondary interference peaks. The results are in good agreement with theoretical calculations, giving evidence to a degree of smoothness and coherency on the scale of atomic dimensions. Furthermore, the nonuniformity in thickness over a relatively large sample area is shown to be governed by the geometry of the growth system.