We developed a simple method to specify the preferential growth orientation by directional growth on multiple seed crystals with random orientations. The preferential growth orientation is regarded as an optimized seed for restraining polycrystallization during growth of multicomponent bulk crystal. We demonstrated its successful application to multicomponent zone-melting method with a quartz crucible to grow SiGe bulk crystal with uniform composition. By growing polycrystalline SiGe bulk crystal on multiple Ge seed crystals with random orientations, we clarified that < 110 > is the preferential orientation of SiGe as evidenced by the largest increase in the area fraction of {110} planes, while that of {111} planes showed the largest decrease. Based on these results, Ge(110) and Ge(111) single crystals were chosen as seeds to grow SiGe. In contrast to the spread of additional grains during growth on Ge(111), no additional grains were seen to emerge throughout the growth on a Ge(110) seed. This manifests that our original method to determine the preferential orientation and to utilize a seed with the preferential orientation is effective for restraining polycrystallization. (c) 2004 Elsevier B.V. All rights reserved.