Local order in amorphous III-V compounds A1-xBxby electron diffraction, in relation with electronic properties

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Abstract
The structure of flash-evaporated amorphous III-V compound films has been investigated by electron diffraction. Discrimination between alternative models has been based on a simple comparison of the relative peak positions in the interference function i(k) with similar data for computer-simulated models. This criterion suggests that a continuous random-network model with even-membered rings only, relaxed or unrelaxed depending on the compound, may be more appropriate for describing the short-range order. The possibility of 'extrinsic' chemical disorder is discussed in the GaP case. For non-stoichiometric a-Ga1-xSbx samples (x>0.5), radial distribution functions W(r) have been derived and their modifications upon increasing Sb excess, especially those of the first-nearest-neighbour peak, have been analysed. It is shown that most of the excess Sb atoms are incorporated at random with threefold coordination, the features typical of a-Sb beginning to appear in the diffraction patterns for x of the order of 0.69. The proposed model is confirmed by studies of the Raman spectra and of the electronic properties.