Morphology and Transport Rates of Mixed IV–VI Compounds in Micro‐Gravity

Abstract

The positive effects of micro‐gravity on crystal growth and basic properties of the vapor transport reaction were established by analyzing the results of three transport experiments of multicomponent systems performed during the Apollo‐Soyuz mission. The systems employed were GeSe0.99Te0.01‐GeI4 false(Afalse) , GeS0.98Se0.02‐GeCl4 false(Bfalse) , and normalGeS‐GeCl4‐normalAr false(Cfalse) . The crystallographic analysis is based on a direct comparison of space‐ and earth‐grown (prototype) crystals, employing x‐ray diffraction, microprobe, microscopic, and chemical etching techniques. The results demonstrate a considerable improvement of the space‐grown crystals in terms of chemical and crystalline homogeneity, surface morphology, and bulk perfection relative to earth specimens. The confirmation of greater mass transport rates than predicted for diffusion‐controlled transport in micro‐gravity suggests the existence of “thermochemically” induced convective motion in chemical vapor transport systems. The morphological observations indicate, that the presence of different convective components yields turbulence which adversely affects crystal quality as observed on earth. The internal consistency and agreement between our ASTP and Skylab results obtained for several compounds, transport agents, and temperature gradients strongly support the validity of these observations.

Developments in Measuring and Calculating Chemical Vapor Transport Phenomena Demonstrated on Cr, Mo, W, and Their Compounds

“…where n L stands for the gram atomic density of the component L in the gas phase; and n V , total gram atomic density of the solvent atoms in the gas phase (the solvent atom is not present in the solid), he obtained for the flux J L (mol/cm 2 s) of the element L with where η′ L and η′′ L stand for η L at x′′ or x′; n, total molar density of the gas phase (∑ λ n λ ); D, mean diffusion coefficient; x′′, location of the source; and x′, location of the sink. The model was applied to the transport systems Ge/GeX 4 (X ) Br, I), 121 GeSe 0.99 Te 0.01 /GeI 4 , 122 GeSe 0.98 -Te 0.02 /GeCl 4 , 122 and GeS/GeCl 4 /Ar. 122…”

“…The model was applied to the transport systems Ge/GeX 4 (X ) Br, I), 121 GeSe 0.99 Te 0.01 /GeI 4 , 122 GeSe 0.98 -Te 0.02 /GeCl 4 , 122 and GeS/GeCl 4 /Ar. 122…”

“…The binary diffusion coefficients have to be evaluated from the literature data or by calculation. The theory was applied to the transport systems ZnS/HCl, 126 ZnS/I 2 , 127 CdS/I 2 , 128,129 CdTe/I 2 , 130 CdTe/NH 4 Cl, 131,132 YbAs/I 2 , 133 GeSe 0.99 -Te 0.01 /GeI 4 , 122 GeSe 0.98 Te 0.02 /GeCl 4 , 122 and GeS/GeCl 4 / Ar. 122…”

“…210 The growth of crystals and epitaxial layers is influenced by convection, too. Investigations of the effects on the morphology of crystals and layers grown by chemical transport reactions under the influence of convection are reported in the transport systems GaAs/GaI 3 , 211 GeSe/GeI 4 , 212,213 Hg 1-x Cd x Te/ HgI 2 , [214][215][216][217][218] GeSe/I 2 , 219 GeSe 2 /I 2 , 219 GeTe/I 2 , 219 GeTe/ GeI 4 , 213 ZnTe/I 2 , 220 MnSe/CdSe/I 2 , 221 GeSe 0.99 Te 0.01 / GeI 4 , 122 GeSe 0.98 Te 0.02 /GeCl 4 , 122 and GeS/GeCl 4 /Ar. 122 A more general theoretical treatment of convection is given by Carruthers, 222,223 Launay and Roux, 224 Reed et al, 209 and Rosenberger et al [225][226][227][228][229][230] There is only one attempt at a detailed analysis of convective flow given by Klosse and Ullersma 231 (KU model).…”

Micrometric single crystal germanates obtained using a double‐spherical mirror furnace

“…These systems were very popular due to the high-temperature operation, through heating achieved by focusing radiation from a lamp; an extremely high purity can be achieved; it can be used selectable atmospheres and pressures; additionally, viewing screen allows monitoring of crystal growth process. Finally, they are compatible with the spatial, physical requirements and safety restrictions in spacecraft [3][4][5][6]. The main application of MF is growth single crystals of high temperature superconductors, dielectric and magnetic materials, pure metals and metallic compounds and different experiments related to microgravity environment (space flight) [7, 8].…”