Mixed cells in directional solidification of In-doped GaAs; cellular profile and shape-induced stresses

Abstract

By revealing the built-in rotation striations in In-doped GaAs grown by the Czochralski technique, X-ray topography enables one to follow the time evolution of the solid-liquid interface. The birth, amplification and lateral spreading of morphological instability and the dynamics of formation of the cellular pattern are analysed. Mixed cells, composed of {111} facets linked together by rough parts, are observed to form and continuously increase in size through facet expansion. Besides, critical information on shape-induced stresses and defects is for the first time obtained. Indeed, additional contrast lines show up close to the facet edges, which can be attributed to peaks in the stress field, induced by the very peculiar profile of the rough regions adjacent to the facets. It follows from the observation of cell eliminations that the contrast lines actually separate these rough regions in two parts: one like the classical equilibrium one, i.e. probably as 3/2, with x the distance from the static facet edge, and one created by the dynamical roughening of the facet, whose edges thus recede from their equilibrium positions.