SURFACE-DIFFUSION AND STEP-BUNCHING MECHANISMS OF METALORGANIC VAPOR-PHASE EPITAXY STUDIED BY HIGH-VACUUM SCANNING-TUNNELING-MICROSCOPY

On a very flat GaAs surface we grow a 1/6 monolayer amount of GaAs by metalorganic vapor-phase epitaxy and observe two-dimensional (2D) nuclei by high-vacuum scanning tunneling microscopy. From the 2D nucleus densities we calculate the surface diffusion coefficient of 2x10(-6) cm(2)/s at 530 degrees C. During growth, the bunched step (multistep) separation saturates and is independent of the substrate misorientation angle. These results can be explained by a mechanism that takes into account both 2D nuclei formation on a wider terrace and their coalescence on ascending steps. A step-bunching simulation based on our model reveals that the saturated multistep separation is proportional to the 2D nucleus separation, i.e., the inverse of the square root of the density. (C) 1995 American Institute of Physics.