Epitaxial Bi(111) films on Si(001) : strain state, surface morphology, and defect structure

Smooth and epitaxial thin bismuth (Bi) films with low defect density were grown on Si(001) by molecular beam epitaxy. The film quality is characterized by in situ spot profile analysis low-energy electron diffraction and scanning tunneling microscopy, and ex situ atomic force microscopy and X-ray diffraction. The complete process is accomplished in three steps. Firstly, a template of a strained 6 nm Bi(111) film is grown at 150 K. Secondly, during annealing to 450 K the strain is relieved by the formation of an ordered array of misfit dislocations at the interface. Finally, additional Bi is deposited at 450 K up to the desired thicknesses of the Bi film. The film consists of 90° rotated and twinned μm size crystallites with a terrace size larger than 100 nm and an overall roughness of only 0.6 nm. A 25 nm thick Bi film is relaxed to Bi bulk lattice constant which is confirmed by X-ray diffraction.