Growth Of Heteroepitaxial Films Research Articles

Summary of in situ epitaxial nucleation and growth measurements

Semiconducting single-crystal thin films of PbSe and chemically prethinned samples of bulk Si were found to be suitable substrate materials for in situ TEM studies of autoepitaxial and heteroepitaxial film nucleation and growth processes. In situ surface cleaning by either evaporation or sputtering was used in conjunction with a UHV background environment to ensure reliable results. The epitaxial systems which have been studied most extensively are Au and Ag on (100)-oriented PbSe. Detailed results obtained include (a) identification of structure (polymorphism), crystalline perfection, and stoichiometry of the initial and the autoepitaxially thickened PbSe substrates; (b) quantitative nucleation and growth kinetic measurements at low supersaturation of Ag on PbSe—a system characterized by weak interaction energies and high surface mobilities; (c) observations of epitaxial orientations and the development of epitaxy during the deposition process; and (d) demonstration of strong substrate/overgrowth reactions involving alloying and interdiffusion.

Heteroepitaxial growth of single crystal films of YIG on GdGaG substrates by hydrothermal synthesis

Heteroepitaxial growth of thin single-crystalline YIG films has been performed by hydrothermal synthesis using GdGaG single crystals as seed plates. Several solvant solutions and varied nutrient materials were tested. The best results were obtained in reacting FeNaO 2 and Y(OH) 3 at 500 °C and 1 kbar with 30° temperature gradient and 5 to 20% baffle opening. Good quality films were obtained particularly for seeds in (211) and (110) orientations. When the films were no more than 30 μm thick, they were transparent with a green color. Under polarized light, some films show very regular band shaped domains.

Rotation and Translation of Islands in the Growth of Heteroepitaxial Films

A simple yet realistic model is introduced for the description of islands of epitaxial overgrowth on a substrate surface. The model is employed to examine the potential energy surface for both rotation and translation of the islands as a whole. It is shown that one or more overwhelmingly easy directions of orientation exist, and that islands which manage to be rotated out of these easy directions can both rotate and translate with activation energies of the order of magnitude of the activation energy for surface diffusion of isolated atoms. The results provide semiquantitative support for Bassett's observation via the electron microscope that large islands of overgrowth (∼1000 atoms) seem to both rotate and translate. Considerations of surface nucleation indicate that although nucleation rate depends on orientation, subsequent growth of islands does not. A growth law independent of orientation is then derived. It is also shown semiquantitatively that under typical experimental conditions for slow deposition, nucleation occurs but once—islands initially formed grow, while their number remains constant. This result is also consistent with several observations. The process by means of which misoriented islands anneal by rotational diffusion into the easy orientation, while they simultaneously grow, is analyzed. A formula is developed which indicates that under certain conditions, islands of overgrowth become ``stuck'' in misoriented positions before they coalesce. The conditions effecting this phenomenon are discussed. General comments and observations are made concerning the initial origin of misoriented nuclei, and means are suggested for adjusting conditions so as to permit misorientation to anneal before coalescence. Typical densities of dislocations introduced by misorientation are estimated. Crucial experiments are suggested for examining the hypothesis of this paper.