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| Author(s): |
Gustavo Martini Dalpian
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física (IF/SBI) |
| Defense date: | 2003-08-11 |
| Examining board members: |
Adalberto Fazzio;
Armando Corbani Ferraz;
Gennady Gusev;
Ricardo Wagner Nunes;
Wagner Nunes Rodrigues
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| Advisor: | Adalberto Fazzio |
| Abstract | |
Using ab initio methods, based on Density Functional Theory, we have systematically investigated problems of interest for semiconductor physics: (i)The SixGe1-x alloy: we observe a small bowing in the lattice parameter, as a function of concentration, and that a larger variation in interatomic distances occurs for Ge-Ge bonds. The behavior of vacancies in this alloy is intermediate between Si and Ge, with formation energies (EF) varying from 2,06 eV to 2,90 eV, depending on the neighborhood of the vacancy. We propose a model for the diffusion of Ge in this alloy. As the vacancy with four Ge atoms as first neighbors hás smaller formation energy, the diffusion of the vacancies Will take place along paths that resemble purê Ge, for Ge-rich alloys; (ii)Surfaces: we study the adsorption of Ge monomers and dimers on Si(100). For monomers, there are several local mínima of the potential energy surface, for the same (x, y) position in the surface, depending on the buckling of the surface dimers near the adatom. We show that this can be identified in theoretical STM (Scanning Tunelling Microscopy) images. This kind of effect also occurs for dimers, and hás already been observed experimentally, but with a wrong interpretation. Through our study, we propose a new structure for the experimental images. The behavior of Si and Ge atoms and dimers near steps is also analyzed. Due to the differencein the lattice parameter of Si and Ge, we show that the adsorption becomes different when only two atoms are in the surface. Through these results, we propose a model to explain the reversion of step roughness due to Ge deposition on Si(100); (iii)Mn impurities in Si: we analise the behavior of Mn impurities in bulk Si ando n the surface. For the bulk, we observe that EF is lower for intersititial than for substitutional sites. On the surface, there is a substitutional site that hás the same EF AS A INTESTITIAL ONE. This fact may be important to the development of Si based ferromagnetic semiconductors. A method is proposed to verify this fact experimentally, through STM images. (AU) | |