Surface diffusion during molecular beam epitaxy was studied. Firstly, the mode transition between 2-dimensional nucleation and step flow during molecular beam epitaxial growth on vicinal surfaces was studied theoretically and experimentally. The basis of the theory was to assume that the transition occurred when the surface supersaturation on the step terrace became identical to the critical supersaturation for 2-dimensional nucleation. This permitted the diffusion length of Ga to be calculated at the experimentally determined critical temperature for the mode transition. It was found that the diffusion length increased, as the temperature decreased, due to an increased residence time. Also, the diffusion length on (111)B was longer than that on (001) when the same formation energy for 2-dimensional nuclei was assumed for both surfaces. The theory was then used to elucidate the dependence of the InGaAs composition upon the growth temperature, the substrate orientation, and the degree of misorientation. The theory gave good agreement with the present experimental data, and it was concluded that surface diffusion was one of the most important processes controlling molecular beam epitaxial growth and impurity incorporation.

T.Nishinaga, T.Shitara, K.Mochizuki, K.I.Cho: Journal of Crystal Growth, 1990, 99, 482-90