Stacking faults and twins in gallium phosphide layers grown on silicon

The coalescence of GaP islands, grown on Si(001), Si(111), Si(110) and Si(113) surfaces by chemical beam epitaxy, has been investigated by high-resolution transmission electron microscopy. Stacking faults and first-order twins are observed within islands before coalescence and result from stacking errors during growth on the smaller P-terminated {111} facets of GaP islands. Upon island coalescence, complex moire fringes are observed contiguous to highly faulted {111} planes within epitaxial layers grown on all four Si substrate orientations and are attributed to multiple (winning. Second- and third-order twins are also observed within (111) and (110) layers and their formation is attributed to successive twinning on differently inclined {111} facets. Amongst the four orientations. coalesced growths on the Si(111) surface are the most defective and this may be caused by a higher density of P-terminated {111} facets on islands grown on the Si(111) surface.