THE DYNAMICAL TRANSITION TO STEP-FLOW GROWTH DURING MOLECULAR-BEAM EPITAXY OF GAAS(001)

Scanning tunneling microscopy studies have been performed on GaAs homo epitaxial films grown by molecular-beam epitaxy. Images show that in t he earliest stages of deposition the morphology oscillates between one with two-dimensional islands and flat terraces. After the initial tra nsient regime, the system evolves to a dynamical steady state. This st ate is characterized by a constant step density and as such the growth mode can be termed step flow. Comparison with RHEED shows that there is a direct correspondence between the surface step density and the RH EED specular intensity. Furthermore, thick films (up to 1450 monolayer s) display a constant or slowly increasing surface roughness consisten t with long adatom diffusion lengths and limited upward diffusion.