Growth-front instabilities in solid-state recrystallization of amorphous GaAs films

Results of the observation of growth-front morphologies during solid-state recrystallization of implanted amorphous GaAs are reported. Discrete growth at small length scales and continuous instabilities at large length scales are simultaneously observed for the first time in the solid phase. In the initial stages of recrystallization, the growth front is made of a rough pattern of recrystallized material on the scale of 10--15 A{}. In a later stage, parabolic instabilities of the growth front appear. The interface roughness increases as the square root of the recrystallized thickness. This dependence is obtained by in situ optical reflectivity experiments. Diffusion of defects in the amorphous layer together with defect reaction at the interface are shown to support well the new experimental data.