After depositing 1/6 of a monolayer of AlAs onto a very flat GaAs (001) surface by means of metal-organic vapor-phase epitaxy, a study was made of AlAs 2-dimensional nuclei by means of high-vacuum scanning tunnelling microscopy. The AlAs 2-dimensional nuclei elongated in the [110] direction, like GaAs. The density of AlAs 2-dimensional nuclei in the saturation region was 5 x 1010/cm2 at 580C. The saturated AlAs 2-dimensional nucleus density decreased with increasing temperature. On the basis of the saturated AlAs 2-dimensional nucleus densities, the surface diffusion coefficient of AlAs on GaAs was estimated to be 1.5 x 10-7cm2/s at 530C. This was an order of magnitude lower than that of GaAs on GaAs.

M.Kasu, N.Kobayashi: Applied Physics Letters, 1995, 67[19], 2842-4