The Effect of Substrate Misorientation on the Evolution of Surface Morphology in Epitaxially Grown CaF2/Si(111) Heterostructures

ABSTRACTWe have studied the effect of substrate misorientation on the evolution of surface morphology in lattice-mismatched heterostructures for molecular beam epitaxial growth of a thin insulator (CaF2) on vicinal Si(111) surfaces with in-situ reflection high energy electron diffraction (RHEED) and ex-situ atomic force microscopy (AFM). At a substrate temperature of 770 °C, CaF2 growth is initiated by the formation of a reacted CaF layer followed by the complete overgrowth of an additional CaF2 monolayer (ml). However, CaF2 growth beyond these two ml depends on the degree of miscut of the Si substrate. On Si substrates tilted toward the [112] by a miscut angle ≥ 0.5°, the atomic step edges on the Si surface bunch together forming flat terraces that are ∼200 nm wide. In this case, the CaF2 growth beyond 2 ml proceeds by the nucleation and lateral propagation of thick CaF2 islands (whose height is determined by the step bunches) along the bunched step edges to eventually form a complete overlayer. For CaF2 films grown on substrates with a miscut angle < 0.5°, the CaF2 layer remains relatively uniform without the formation of thick islands. With further deposition, evidence for a dense network of misfit dislocations is observed on the surface of the CaF2 film.