Structure and physical properties of paracrystalline atomistic models of amorphous silicon

We have examined the structure and physical properties of paracrystalline m olecular dynamics models of amorphous silicon. Simulations from these model s show qualitative agreement with the results of recent mesoscale fluctuati on electron microscopy experiments on amorphous silicon and germanium. Such agreement is not found in simulations from continuous random network model s. The paracrystalline models consist of topologically crystalline grains w hich are strongly strained and a disordered matrix between them. We present extensive structural and topological characterization of the medium range order present in the paracrystalline models and examine their physical prop erties, such as the vibrational density of states, Raman spectra, and elect ron density of states. We show by direct simulation that the ratio of the t ransverse acoustic mode to transverse optical mode intensities I-TA/I-TO in the vibrational density of states and the Raman spectrum can provide a mea sure of medium range order. In general, we conclude that the current paracr ystalline models are a good qualitative representation of the paracrystalli ne structures observed in the experiment and thus provide guidelines toward understanding structure and properties of medium-range-ordered structures of amorphous semiconductors as well as other amorphous materials. (C) 2001 American Institute of Physics.