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Theoretical Studies of Amorphous and Paracrystalline Silicon

Nakhmanson, Serge M.
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou984426180

Abstract Details

2001, Doctor of Philosophy (PhD), Ohio University, Physics (Arts and Sciences).
Until recently, structural models used to represent amorphous silicon (a-Si) in computer simulations were either perfectly fourfold connected random networks or random networks containing only miscoordinated atoms. These models are an approximation to the structure of the real material and do not uniformly comply with all the experimental data for a-Si. In this dissertation we make an attempt to go beyond this approximation and construct and examine models that have two major types of defects, encountered in real material, in their structure - nanovoids and crystalline grains. For our study of voids in a-Si we have calculated vibrational properties of structural models of a-Si with and without voids using ab initio and empirical molecular dynamics techniques. A small 216 atom and a large 4096 atom continuous random network (CRN) models for a-Si have been employed as starting points for our a-Si models with voids. Our calculations show that the presence of voids leads to an emergence of localized low-energy states in the vibrational spectrum of the model system. Moreover, it appears that these states are responsible for the anomalous behavior of system's specific heat at very low temperatures. To our knowledge these are the first numerical simulations that provide adequate agreement with experiment for the very low-temperature properties of specific heat in disordered materials within the limits of harmonic approximation. For our study of crystalline grains in a-Si we have developed a new procedure for the preparation of physically realistic models of paracrystalline silicon based on a modification of the bond-switching method of Wooten, Winer, and Weaire. Our models contain randomly oriented c-Si grains embedded in a disordered matrix. Our technique creates interfaces between the crystalline and disordered phases of Si with an extremely low concentration of coordination defects. The resulting models possess structural and vibrational properties comparable with those of good CRN models of a-Si and display realistic optical properties, correctly reproducing the electronic bandgap of a-Si. The largest of our models also shows the best agreement of any atomistic model structure with fluctuation microscopy experiments, indicating that this model has a degree of medium-range order closest to that of the real material.
David Drabold (Advisor)
190 p.
Physics, Condensed Matter
amorphous silicon; paracrystalline silicon; computer simulation; atomistic model; structural model

Recommended Citations

Citations

  • Nakhmanson, S. M. (2001). Theoretical Studies of Amorphous and Paracrystalline Silicon [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou984426180

    APA Style (7th edition)

  • Nakhmanson, Serge. Theoretical Studies of Amorphous and Paracrystalline Silicon. 2001. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou984426180.

    MLA Style (8th edition)

  • Nakhmanson, Serge. "Theoretical Studies of Amorphous and Paracrystalline Silicon." Doctoral dissertation, Ohio University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou984426180

    Chicago Manual of Style (17th edition)

ohiou984426180
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© 2001, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.