Effect of Twin Boundary Formation on the Growth Rate of the GaSb{111} Plane

The top surface of a crystal-melt interface was observed directly during directional solidification of polycrystalline GaSb at a constant cooling rate, and the effect of {111}Σ3 twin boundary formation on the rate of grain growth parallel to the direction was investigated. A {111}Σ3 twin boundary was generated by the decomposition of another {111}Σ3 twin boundary with formation of a Σ9 grain boundary. The growth of the crystal-melt interface in the direction parallel to the B direction was stalled during the nucleation and propagation of the new {111}Σ3 twin boundary. The growth rate of the crystal-melt interface after twin formation was approximately half of that before. This is considered to be due to {111} polarity reversal by twinning. The dangling bond density on the{111}A plane of GaSb is almost ten times of that on the {111}B, and the dangling bond density is related to the attachment energy of atoms of the plane; therefore, the growth rate in the A direction would be significantly lower than that in the B direction. These results indicate different growth rates in opposite directions and a significant effect of the polarity on the competition of grain growth during the directional solidification of polycrystalline GaSb.