Structure of the (110) antiphase boundary in gallium phosphide

The morphology of antiphase boundaries in GaP films grown by molecular beam epitaxy on Si (001) has been studied by transmission electron microscopy. The inversion of the crystal polarity between antiphase domains was confirmed by convergent-beam electron diffraction. The APBs were often found to facet parallel to [110] planes. Strong-beam alpha-fringe contrast observed along the (110) facets indicates that adjacent antiphase domains are related by an additional rigid-body lattice translation. Diffraction-contrast analysis shows that this R corresponds to a shear parallel to the [001] direction and a small expansion. The magnitude of the translation was inferred, quantitatively, through a comparison between energy-filtered zero-loss images of the alpha-fringe contrast with numerical calculations. The components of the rigid-body lattice translation were determined to be 0.023 +/- 0.0033 nm in the [001] direction and 0.005 +/- 0.002 nm in the 0 direction. Based upon a geometric model of the [110] antiphase boundary, the lengths of the Ga and P antisite bonds were calculated to be 254 +/- 2 pm and 227 +/- 4 pm, respectively.