Characterization of gallium antimonide crystals grown under microgravity conditions by the Liquid Encapsulated Melt Zone (LEMZ) technique

A Liquid Encapsulated Melt Zone (LEMZ) technique was used to grow [100] GaSb single crystals under microgravity conditions aboard the STS-77 Shuttle Endeavor mission. One tellurium-doped and two undoped single crystals, encapsulated in a eutectic mixture of sodium-chloride and potassium-chloride, were regrown from 16 mm diameter single crystal rods. The quality of the crystals was compared to those grown on ground using the same technique. It was found that the microgravity-grown crystals, particularly the Te-doped crystal, exhibited lower dislocation densities than those grown on ground. The dislocation density was also found to depend on the solid/liquid interface shape with a planar interface resulting in a lower density. Reduction of rotational and nonrotational striations was obtained with the encapsulation technique in all crystals. Moreover, the use of the encapsulant allowed for longer and more stable melt zones for those samples processed on ground.;Macrosegregation of the tellurium dopant revealed that convective-controlled growth occurred in both microgravity and terrestrial environments. The use of an encapsulant helped control but did not eliminate Marangoni convection and/or convection caused by variations in the gravity level. Irregular radial dopant distribution in the microgravity sample was attributed to localized convective flows at the growth interface caused by uneven heating when the sample was pushed off its growth axis by an argon bubble in the ampoule.;Hall and photoluminescence measurements confirmed the high quality of the crystals, but revealed that growth under different gravity environments did not influence their electrical or optical properties. However, several results from this study were highly useful in helping to understand the lesser studied gallium antimonide material system itself. Variable temperature Hall and photoluminescence measurements in the undoped crystals found two dominant acceptors at 12.5 and 33 meV below the bandgap edge. The temperature variation of the latter peak compared to the bandgap edge was explained by either a true decrease in the ionization energy of this level or by a variation in the photoabsorption capture cross section which is different than most other semiconductors. In the n-type samples, Hall measurements were used to calculate the energy level of the subsidiary conduction band and its temperature variation.