Morphological evolution during molecular beam epitaxy of germanium/germanium(001) and silicon/germanium(111).

摘要

The evolution of morphology and microstructure during Ge homoepitaxial growth, especially at low temperatures of 150°C to 250°C, is strongly influenced by the growth kinetics. Morphological evolution on singular and vicinal surfaces is driven by instabilities during epitaxial growth. In my experimental study, I have investigated the influence of substrate vicinality and atomic hydrogen exposure on the Ge(001) epitaxial morphology.; Vicinal surfaces of varying miscut are created on singular Ge(001) substrates by laser texturing. Epitaxial growth on these textured surfaces show a morphological transition from mound structures on singular surfaces to ridge structures on vicinal surfaces miscut along 110> for miscut angles >2°. For Ge film thickness of 50 to 450 nm deposited in the temperature range of 150°C to 250°C the root-mean-square (rms) roughness of the ridges increases with miscut angle (from 0.3 nm to 1 nm), while the lateral roughness length scale decreases with miscut.; I have studied the influence of atomic hydrogen during low temperature epitaxy (150°C to 300°C) on singular and vicinal Ge surface. Atomic hydrogen adsorbs on Ge surfaces and reduces the surface diffusion of Ge adatoms during epitaxial growth. Atomic hydrogen exposure during epitaxy changes the mound morphology of epitaxial structures to a planar surface on singular Ge(001). Despite the morphological transition to a smoother surface, the epitaxial thickness is reduced at 150°C from ≈430 nm to 35 nm.; I have investigated the evolution of islands during the heteroepitaxy of Si on Ge(111). This study involves a systematic investigation of the island nucleation kinetics, morphology and microstructure for various thicknesses and deposition temperatures. The islands formed are predominantly three-dimensional. A large density of islands (>1011 cm−2) is observed during growth at low temperatures (550°C) and growth at higher temperatures (>600°C) yield a lower density of islands. The activation energy for the nucleation of these islands is ≈1.7 eV. The islands deposited at temperatures 550°C are predominantly coherent, while those formed at higher temperatures are incoherent, with a transition size of ≈18 nm.