Reflection electron microscopy study of structural transformations on a clean silicon surface in sublimation, phase transition and homoepitaxy

Abstract

Reflection electron microscopy has been applied to in situ study of silicon sublimation, phase transition and homoepitaxy. Reversible rearrangement of the stepped Si(111) surface from a regular monoatomic step system to step bunching was observed. These transformations were found to depend on the temperature and direction of the electric current heating the crystal. The redistribution of about 4 × 10¹⁴ cm⁻² atoms on the Si(111) surface during (7 × 7) (1 × 1) phase transition has been established by the displacement of monoatomic steps and a change in size of two-dimensional sublimation and growth islands under this transition. The relation between the areas of the Si(001) surface having the structures (1 × 2) and (2 X 1) has been observed to depend on the direction of electric current heating the crystal. The anisotropy of the adatom diffusion on Si(001) surface has been shown. During homoepitaxy on Si(111) the intensity oscillations of the specular electron beam have been shown to be caused by the periodic changes of the surface micromorphology due to the growth of two-dimensional islands. One oscillation period corresponds to the growth of one monolayer. The areas adjacent to monoatomic step have been observed to be free from two-dimensional islands. Contrast analysis of REM images obtained by $\text{1}\text{7}$ order reflection shows that these areas on the upper terrace of step are characterized by the (7 × 7) structure, but the structure of areas free from islands on the lower terrace is (1 × 1). Analysis of individual monoatomic step motion during sublimation, phase transition and homoepitaxy showed that the energetic barrier for the incorporation of adatoms into the monoatomic step from the lower terrace is less than that from the upper terrace.