CHANGES IN THE MOIRE PATTERNS IN ELECTRON-MICROSCOPE IMAGES OF AS CLUSTERS IN LT-GAAS AS THEIR SIZE DECREASES

Electron microscope studies are made of gallium arsenide obtained by l ow-temperature (200 degrees C) molecular beam epitaxy (LT-GaAs) in whi ch the excess arsenic is precipitated out by annealing at 600 degrees C. A moire technique is used to show that reducing the size of the As clusters from 10-12 to 3 nm leads to significant variations in the int erplanar separations of the original arsenic hexagonal structure, Thes e changes are inconsistent with a deformation effect on the LT-GaAs ma trix and appear to be caused by the fact that the small (<3 nm) cluste rs have a cubic structure. The realignment of the atomic structure of the arsenic clusters may have important consequences for explaining th e insulating properties of LT-GaAs. (C) 1996 American Institute of Phy sics.