In-situ STM studies of multilayer Ge quantum dots and Si nanopatterning on Si(001)

Abstract

Scanning tunneling microscope (STM) was used to investigate the evolution and ordering of multi-layer (upto 14 layers) Ge islands on Si(001) prepared by physical vapor deposition at about 550 A?C. We have observed that the first-layer Ge islands are huts- and pyramidal-like, bounded by {105} facets. Its sizes range from 10 to 15 nm while its heights are in the order of 2 nm in average. In the growth process, it was observed that long huts split during the deposition of Si buffer layer. The splitting of Ge islands can be explained as a consequence of strain due to lattice mismatch and intermixing of Si and Ge to form solid solution. Such a mechanism of splitting could lead the dots to order and uniform in the subsequent layers. Apart from splitting of huts, the surface corrugation of Si spacer layer influences the nucleation of Ge islands in the next layer. Recently, in the intermediate study of Si homoepitaxy we found that a steady state in which the surface roughness reaches a saturate value after a transition period is achieved. This is monitored with in situ STM. Within this steady state range, the dominant surface morphology varies from double layer steps to nearly square nano-meter scale multi-layer vacancy islands (pits) isolated by connected smooth area on top. These vacancy (pits) obtained in steady-state epitaxy growth can be used as templates for fabrication of other nanostructure such as Ge quantum dots.