OBSERVATION OF QUASI-PERIODIC FACET FORMATION DURING HIGH-TEMPERATURE GROWTH OF ALAS AND ALAS/GAAS SUPERLATTICES

Quasi-periodic facetting has been observed during high temperature, molecular beam epitaxial-growth of AlAs and AlAs/GaAs superlattices. The facetting is shown to be related to the thickness of the AlAs epilayers and is unrelated to the number of interfaces in the superlattices. The observed facetting is also shown to be dependent on the substrate temperature. Reflection high-energy electron diffraction patterns monitored during growth change from streaky to spotty, indicating a three-dimensional growth surface. Chevrons can clearly be seen when the electron beam is directed along a [011] azimuth, indicating a particular crystallographic plane is now dominant on the surface and is aligned along that azimuth. Cross-sectional transmission electron micrographs confirm that the surface has facetted, forming a quasi-periodic triangle pattern with a period of about 1800 angstrom.