| The epitaxial growth of Ge on Si substrates was carried out using surfactant-mediated epitaxy and standard growth procedures to study the effects of Si surface passivation prior to Ge nucleation. The growth experiments were conducted in a molecular beam epitaxy (MBE) chamber equipped with reflection high-energy electron diffraction (RHEED) to monitor the nucleation process. Arsenic was chosen as the surfactant material and Ge nucleation was conducted on both Si(001) and Si(211) orientated substrates. Post-growth experiments were conducted primarily utilizing Raman Spectroscopy, however scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction were also employed to gather information about the grown material.; From these experiments, it was determined that passivating the Si surface prior to Ge deposition with a monolayer of As yields higher quality 2-dimensional material. Additionally, As acts as a suppressant to Ge - Si intermixing resulting in a highly ordered epilayer/substrate interface. If Ge is deposited directly on a clean Si substrate without As passivation, the resultant growth follows the theoretically predicted Stranski-Krastanov growth mode. A growth model is suggested that successfully describes the differences between surfactant-mediated and non-surfactant-mediated nucleation through a site-exchange mechanism between Ge and As atoms. Additionally, surfactant-mediated nucleation results as a function of substrate orientation are highlighted and a model for surface reconstruction of the As passivated Si(211) surface is proposed. |
