Local lattice parameter determination of a silicon (001) layer grown on a sapphire (11̄02) substrate using convergent-beam electron diffraction

All the six lattice parameters (a, b, c, α, β and γ) of a Si (001) layer grown on a sapphire (1$\overline 1$02) substrate were determined by convergent-beam electron diffraction with no assumption of crystal lattice symmetry. A lattice compression in the Si (001) plane and an elongation in the [001] direction were revealed. An anisotropic lattice compression in the (001) plane was clearly detected for the first time. That is, the lattice compression in the Si [100] direction, which is parallel to the sapphire [$\overline 1$101] direction, was larger than that of the Si [010] direction, which is parallel to the sapphire [$\overline 1$$\overline 1$20] direction. It was also revealed that the lattice parameters of the Si-layer depend on the distance from the interface. Anisotropy of carrier mobility was reasonably explained in terms of the anisotropy of the lattice parameters determined.