The recent advancement in the in situ scanning electron microscopy of molecular beam epitaxy of GaAs is reviewed. The topics include two-dimensional (2D) nucleation and growth, three-dimensional (3D) roughening processes, 2D-to-step-propagation growth mode change and annealing processes after growth. In the nucleation-and-growth mode, delayed island nucleation and nonlinear change of surface coverage are found. The mechanism of delayed nucleation is discussed in terms of site-dependent successive atomic layer growth processes. It is shown that under a critical growth condition between the 2D mode and the step propagation mode, the local growth mode changes from the 2D mode to the step propagation mode. It is found that there are three types of surface roughening, or onset of 3D growth. A 3D/2D/1D growth mode phase diagram is obtained. Some of the results are compared with the growth of Si on (111) surface. The behavior of monolayer-deep holes during postgrowth annealing is observed. It is found that some holes are left for a long time and form big holes with each other. They extend in the [110] direction but, at the same time, shrink in the [1-10] direction. Finally, they shrink in both directions and disappear .It takes about 10 min for all the holes to disappear. Related work by other authors is briefly described.
