Misoriented Epitaxial Growth of (111)CoSi_2 on Offset (111)Si Substrates

Abstract

Single crystal epitaxial films of CoSi_2 were grown by MBE on various (111)Si single crystal substrates, whose surfaces were purposely tilted towards the <110>_g, direction by small angles ϕ_g,†, 0°, ≤ ϕ_g, ≤, 4° measured between the surface normal and the <111>_g, direction of Si. The actual offset angle, ϕ_g was determined by back Laue reflection method. The average perpendicular strain of the CoSi_2 epilayer, ε┵, and the <111>_f orientation of the epitaxial CoSi_2 film were determined by double crystal diffractometry. We find that the misorientation angle, a, measured between the Si <111>_g, and CoSi_2 <111>_f directions, increases linearly with the offset angle, ϕ_g, up to ϕ_g = 4°. A simple geometrical model is developed which predicts that α = ε┵ × tan ϕ_g. The model agrees quantitatively with the experimental data. The equivalent strain energy associated with the misorientation is approximated by that of a low angle tilt boundary. The misorientation angle α of the equilibrium state, determined by minimizing the total strain energy of the epitaxial film, is nonzero in general.