Kinetic Instability of Semiconductor Alloy Growth

Abstract

AbstractA kinetic theory of the instability of homogeneous alloy growth with respect to fluctuations of alloy composition is developed. The growth mechanism studied is the step-flow growth of an alloy from the vapor on a surface vicinal to the (001) surface of a cubic substrate. The epitaxial growth implies that the adsorbed atoms migrate on the surface during growth of each monolayer, and that their motion is “frozen” after the completion of the monolayer. Frozen fluctuations in all completed monolayers create, via the composition-dependent lattice parameter, an effective potential which influences the surface migration of adatoms. The migration consists of diffusion and strain-induced drift in the effective potential. For temperatures lower than a certain critical temperature Tc, strain-induced drift dominates diffusion and results in the kinetic instability of the homogeneous alloy growth. In the linear approximation in the fluctuation amplitude, the instability means the exponential increase of the fluctuation amplitude with the thickness of the epitaxial film. It is shown that the critical temperature of kinetic instability Tc, increases with the increase of elastic effects. The wave vector kc of the most unstable mode of composition fluctuations is determined by the interplay of anisotropic elastic interaction and anisotropic diffusion on a stepped vicinal surface. The direction of the wave vector kc differs from the lowest-stiffness direction of the crystal, and any direction of kc is possible.