IDENTIFICATION OF THE MISFIT DISLOCATIONS AT AN FEAL/ALAS/GAAS INTERFACE USING MOIRE FRINGE CONTRAST IN A TRANSMISSION ELECTRON-MICROSCOPE

Moire fringe contrast in plan-view transmission electron microscopy (TEM) is adapted to measure the Burgers vector of misfit dislocations at the interface between FeAl and AlAs. This technique had originally been used to determine the Burgers vector of dislocations in bulk materials. The aluminide was grown by molecular beam epitaxy on AlAs which was pseudomorphic on GaAs(001). The observed misfit dislocations are determined to have [100] and [010] Burgers vectors, as measured in the FeAl, with [010] and [100] line directions, respectively. These are pure edge dislocations which cannot glide on the {110} or {112} slip systems of FeAl. This requires that the misfit dislocations either form at the edges of islands, during three dimensional (3D) growth or by climb from the free surface during two-dimensional (2D) growth. The TEM results along with in situ reflection high-energy electron diffraction (RHEED) results show that the growth is indeed 2D which suggests the misfit dislocations must form by dislocation half-loops climbing from the free FeAl surface.