Local lattice parameter determination of a silicon (001) layer grown on a sapphire (1(1)over-bar-02) substrate using convergent-beam electron diffraction

All the six lattice parameters (a, b, c, alpha, beta and gamma) of a Si (001) layer grown on a sapphire (1 (1) over bar 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 [(1) over bar 101] direction, was larger than that of the Si [010] direction, which is parallel to the sapphire [(1) over bar(1) over bar 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.