7×7 Superstructure at the Amorphous Si/Si(111) Interface and Its Modification During Solid Phase Epitaxial Growth

Abstract

The 7×7 superstructure buried at the amorphous Si (a-Si)/Si(111) interface was directly observed by transmission electron microscopy (TEM). High-resolution (HR) images of the 〈110〉 cross-sectional observation showed the atomic arrangement of the projected interface superstructure, which had a periodicity of 7 times the 1/3(224) periodicity along the interface. The atomic structure, which consists of a dimer-stacking fault layer and epitaxial layers extended over the vacant corner sites and the dimer-chains, was revealed by using computer image simulation. Structural modification of the interface 7×7 superstructure during solid phase epitaxial growth (SPE) of the a-Si overlayer was also investigated by TEM. Plan-view transmission electron diffraction observations of samples annealed at various temperatures indicated that a modification of the dimer structure occurred during the transformation from the 7×7 to the 1×1 structure (7×7→l×1). It was found by (110) cross-sectional HRTEM that 7×7→1x1 proceeded laterally within the stacking fault layer prior to the vertical SPE of the a-Si. Furthermore, it was confirmed that the unfaulting of the reversed stacking region, as well as the faulting of the normal stacking region, occurred simultaneously during 7×7→1×1. The mechanism of 7×7→1×1 through the dimer modification was also discussed.