THE CORRELATION BETWEEN SUPERHEATING AND SUPERCOOLING IN CDTE MELTS DURING UNSEEDED BRIDGMAN GROWTH

Recently, the crystal growth of semiconducting compounds using a low temperature gradient profile (less-than-or-equal-to 10 K/cm) has gained in interest. In the case of unseeded growth considerable supercooling in the tip region can be observed. These supercooling effects depend on the degree of superheating in the molten state. A decrease in the associated structure of molten CdTe is reflected by a step-like increase in the degree of supercooling for melts superheated by more than about 10 K. A large-extended polycrystalline region can result on crystallization if superheating > 9-10 K is used. This polycrystalline first-to-freeze region is followed by a section of monocrystalline crystal or by a region with only one or two grain boundaries. When a small degree of superheating is used (< 9-10 K) an initial region of monocrystalline growth is often observed. A larger number of grain boundaries, however, subsequently form in the later stages of the growth run.