Crystal Growth and Steady‐State Segregation under Zero Gravity: InSb

Abstract

A B S T R A C TIt was established that ideal, diffusion-controlled, steady-state segregation, never accomplished on earth, was achieved during the growth of Te-doped InSb crystals in Skylab. Surface tension effects led to nonwetting conditions u n d e r which free surface solidification took place in confined geometry. It was further found that, under forced contact conditions, surface tension effects led to the formation of surface ridges (not previously observed on earth) which isolated the growth system from its container. In addition, it was possi~ble, for the first time, to identify unambiguously: the origin of segregation discontinuities associated with facet growth, the mode of nucleation and propagation of rotational t w i n boundaries, and the specific effect of mechanical-shock perturbations on segregation. The results obtained prove the advantageous conditions provided by outer space. Thus, fundamental data on solidification thought to be unattainable on earth because of gravityinduced interference are now within reach.Structural and compositional control during solidification of materials is impeded by gravity-induced effects in the melt. Thermal gradients necessary for crystal growth lead, in the presence of gravitational forces, to thermal convection which in general causes uncontrolled variations in the solidification rate and in diffusion boundary layer thickness; such variations lead directly to periodic and/or random microscopic and macroscopic segregation inhomogeneities. F u rthermore, in the presence of gravity, establishing steep thermal gradients, frequently required to prevent constitutional supercooling, is often impossible and consequently interface breakdown is unavoidable.Gravity effects are, thus, primarily responsible for the present lack of reliable solidification data and the existing gap between theory and experiment. Consequently, crystal growth and associated segregation phenomena are still based on empiricism, and the properties and performance of solids are not at their theoretical limits.Gravity-free conditions made accessible through the space program provide a unique opportunity to obtain reliable crystal growth data and, therefore, to advance our quantitative understanding of solidification processes; in addition this program makes possible the exploration and assessment of the potential of outer space for materials processing.Indium antimonide was chosen for the presently reported Skylab experiment because its relatively low melting point (525~ made the experiment compatible with the available electrical power. In addition, chemical etching, the only high-resolution technique available, at the time, for the study of segregation inhomogeneities on a microscale, had been developed on InSb to its most advanced level.The experiments performed during the Skylab-III and -IV missions included the growth of undoped, tellurium-doped, and tin-doped indium antimonide. The present report is concerned primarily with results obtained on tellurium-doped InSb. ObjectivesThe objectives of...

Two-dimensional numerical simulation of thermocapillary convection in detached solidification

“…Soon afterwards, Witt et al also found the separation growth of crystal when they researched the crystal growth and steady-state segregation of InSb under zero gravity. And they found that the crystal growing from the separate areas in both quality and performances was obviously better than the crystal growing using traditional technology [2]. Since then, Duffar and Regel explained the phenomenon of crystal growth separating from the crucible wall under microgravity condition [3], thus putting forward the detached solidification Bridgman method which combines the advantages of Czochralski method and Bridgman crystal growth method.…”

Non-Lyapunov Type Stability in a Model of the Dewetted Bridgman Crystal Growth Under Zero Gravity Conditions

“…"Dewetting" or "detachment" phenomenon was first observed spontaneously in space experiments during InSb Bridgman solidification performed on Skylab-NASA mission-1974 (Yue andVoltmer 1975;Wilcox et al 1975;Witt et al 1975). In dewetted Bridgman technique, the solid crystal is detached from the crucible wall by a small liquid meniscus at the level of the solid-liquid interface, creating a gap between the grown crystal and the crucible wall.…”

Initial transient in Zn-doped InSb grown in microgravity

“…The diffusion-controlled segregation in microgravity [1] can be disturbed by the residual micro acceleration [2], or bubbles [3,4]. Free surfaces and bubbles create a major disruption in fluid properties (e.g.…”