SURFACE-DIFFUSION AND RELATED PHENOMENA IN MBE GROWTH OF III-V COMPOUNDS

Surface diffusion in MBE is studied taking GaAs and InzGa1-z As as examples. First, the mode transition between 2D nucleation and step flow in MBE on vicinal surfaces is studied theoretically and experimentally. The principal idea of the theory is to assume that the transition occurs when the surface supersaturation on the step terrace becomes identical with the critical supersaturation for 2D nucleation. This allows the diffusion length of Ga to be calculated at the experimental critical temperature for the mode transition. It is found that the diffusion length increases as the temperature is decreased, due to the increased residence time, and that the diffusion length on (111)B is longer than that on (001) using the assumption of equal formation energy of 2D nuclei for both surfaces. Then the theory is applied to help understand the dependence of the InzGa1-zAs composition on the growth temperature, the substrate orientation and the degree of misorientation. The theory is in good agreement with the present experiments and it is concluded that surface diffusion is one of the most important and essential processes controlling MBE growth and impurity incorporation. © 1990.