Experiment Step Research Articles

A TEM and EDS Study on the effect of back melting on directionally solidified HgZnTe

Bulk growth of II-VI semiconductors such as HgZnTe (MZT) is difficult because of the gravity-induced convection that occurs during solidification. This convection can lead to crystal defects (primarily dislocations and subgrain boundaries) and composition inhomogeneities which may limit device performance. Crystals grown in the low-gravity environment of space should have fewer of these defects. However, the limited duration of space shuttle experiments and the need for uniform composition make it imperative that the initial composition transient that occurs in directionally solidified alloys be eliminated. One proposed solution to this problem is back-melting. In the first stage of this process, a section of the specimen is directionally solidified and the remainder is quenched. The quenched portion is then remelted and directionally solidified. In the flight experiment, the remelting and second directional solidification step will be carried out in space.