A mixing experiment of multicomponents melts was performed using a uniform tempcrature furnace in thc Second International Microgravity Laboratories (IML-2) mission. Growth morphologies and Ga concentration profiles were analyzed for the samples with the compositional ratio of 0.5 In-0.5 Ga-1.0 Sb grown under microgravity and on earth. The sample with free surface grown under microgravity was nearly sphcrical in shapc, cxccpt some parts with projections. Ga was dispersed homogeneously in the bulk because the mixing was enhanced by Marangoni convection due to the concentration gradient. On the other hand, the sample grown on earth was a double cylindrical shape with different diameters, and Ga concentration decreased from top to bottom, showing clearly the cffcct of gravity. Many needle crystals were formed in both space and earth samples due to rapid cooling. The average size of the needle crystals grown in space was larger than that of the earth sample.
In order to investigate the effects of diffusion and convection on the melt mixing of semiconductors, experiments under microgravity in space and 1-g on earth were conducted. Sandwich combinations of In/GaSb/Sb solids closed in a BN cylinder were heated up to 733° C in space and 744° C on earth, and they were then cooled rapidly. In both samples, many needle crystals were distributed in the whole area. It was observed that the melt mixing in space was controlled by diffusion which was represented with an error function, and the diffusion coefficient of indium was given by a value of 2.4×10-4 cm2/ s. In the earth sample, however, the indium concentration distribution followed an exponential curve. This indicated that both factors, diffusion and thermal convection, have contributed to the mixing of semiconductor melts.
It has been shown that nanocrystalline silicon films can be grown from silane gas without hydrogen dilution by electron-beam excited plasma chemical vapor deposition (EBEP–CVD). A high density of atomic hydrogen, which is derived from the dissociation of silane molecule, is confirmed in the plasma by optical emission spectroscopy. This fact is thought to be a reason for the growth of nanocrystalline silicon films without the introduction of hydrogen gas. Transmission electron spectroscopy reveals that crystallites are not distributed uniformly, but rather form the mosaic-like clusters in an amorphous silicon matrix in the film. Hydrogen gas is introduced into the EBEP–CVD silicon film growth so as to study the effects of the hydrogen gas. The growth rate increases proportionally to the hydrogen flow rate, and it is about 2.5 times greater than when no hydrogen gas is introduced. Also, a decrease in both the hydrogen content and the density of dangling bonds in the film is confirmed. These results imply that the generation of dangling bonds is suppressed by the introduction of hydrogen. The rate constants of dissociation reaction of silane molecules in the EBEP are estimated, and the change in density of radicals in the plasma by introducing hydrogen gas is calculated. A growth model is proposed that assumes the sticking coefficient of SiH3 precursor radical increases in proportion to atomic hydrogen flux. Using the calculation results and the model, the effects are explained to be due to an increase in the contribution ratio of SiH3 radicals to the growth, on account of the increase in the introduced hydrogen gas flow rate.
Using electron beam excited plasma chemical vapor deposition, nanocrystalline Si films can be grown without H 2 dilution. This paper describes the effects of growth parameters on the growth rate and the crystallinity of Si films.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.