Directional solidification of InSb in a centrifuge

Abstract

Thirteen samples of undoped InSb, InSb doped with tellurium, and InSb doped with selenium were directionally solidified in a gradient freeze furnace mounted at the end of the 18 m long arm of a centrifuge. Each ingot was subjected to a different acceleration during growth. One selenium-doped sample was also solidified in a centrifuge with a 5.5 m arm. The microstructure seemed to depend on the g level and on the doping. An undoped ingot grown at 9 g ( g = 9.81 m/s 2) consisted primarily of a single grain containing a number of twins. With doping, microcracks sometimes occurred, but never without doping. An undoped ingot grown at 7 g, a Te-doped ingot grown at 9 g and a Se-doped ingot grown at 10 g had the fewest number of twins compared to the rest of the ingots. No dopant striations were observed in any of the ingots, indicating that the freezing rate did not fluctuate. The ingots grown in the centrifuge had very few tiny bubbles or in some cases no bubbles on their outer surface. Hall coefficient measurements showed that both Te and Se-doped ingots were n-type. Resistivity of undoped and doped InSb ingots decreased with increase in temperature, while mobility increased with increase in temperature. The hole concentration in undoped InSb grown at 9 g was constant along the length of the ingot.