ON SPINODAL DECOMPOSITION IN ELASTICALLY ANISOTROPIC EPITAXIAL-FILMS OF III-V SEMICONDUCTOR ALLOYS

The elastic energy associated With alloy composition modulation in the epitaxial film of a III-V semiconductor alloy on the [001]-substrate is calculated in the analytic form. Composition modulation both in the directions parallel to the substrate surface and in the growth direct ion are taken into account. It is shown that the minimum of the elasti c energy corresponds to the modulation along the [100] (and/or [010]-) direction, the period of the modulation d being small compared to the film thickness h (d much less than h). The ''soft mode'' of compositi on modulation is exponentially localized near the free surface, the lo calization length l being l = d/2pi. The elastic energy caused by this modulation is less by the factor 1/2c11/(c11+c12) than the elastic en ergy corresponding to spinodal decomposition in the bulk sample. This factor is almost-equal-to 1/3 for III-V alloys. Critical temperatures of spinodal decomposition T(c) are calculated for a number of epitaxia l ternary III-V alloys. The diffusion which occurs only in the very th in subsurface layer (nearly monolayer) is shown to provide exponential amplification of the composition modulation amplitude deltac(0) appro ximately exp (DELTAh/l) at early stages of the subsequent layer-by-lay er growth.