Adsorption and growth on Si(001) surface

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Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Fen Bilimleri Enstitüsü, Türkiye

Tezin Onay Tarihi: 2004

Öğrenci: RİAD SHALTAF

Danışman: SÜLEYMAN ŞİNASİ ELLİALTIOĞLU

Özet:

The (001) surface of silicon has been the topic of our study in this thesis. The clean surface, an-adatom or submonolayer adsorption on the surface, the monolayer adsorption and its stability conditions as well as growth simulation on the surface were investigated using the state of the art techniques. We have used ab initio density functional calculations based on norm-conserving pseudopotentials to investigate the Mg adsorption on the Si(001) surface for 1/4, 1/2 and 1 monolayer (ML) coverages. For both 1/4 and 1/2 ML coverages it has been found that the most favorable site for the Mg adsorption is the cave site between two dimer rows consistent with recent experiments. For the 1 ML coverage (2 Mg atoms per 2X1 unit cell) we have found that the most preferable configuration is when both Mg atoms on 2X1 reconstruction occupy the two shallow sites. We have found that the minimum energy configurations for 1/4 ML coverage is a 2X2 reconstruction while for the 1/2 and 1 ML coverages they are 2X1. Same method was also used to investigate the surface stress and energetics of the clean-, Sb-adsorbed-, and Sb-interdiffused-Si(001) surface. It is found that interdiffusion of Sb into deeper layers of Si(001) leads to a more isotropic surface stress but corresponds to a higher total energy configuration. As a result of competition between stress relief and energy gain, the surface with all the Sb atoms adsorbed on top of Si(001) surface layer is predicted to have a less ordered geometry and roughness in z-direction. We have repeated the similar calculations on the Ge(001) surface for comparison. Finally using empirical molecular dynamics method, we have investigated the crystalline growth of silicon on Si(001) as a function of substrate temperature and incident particle energy. Our results show that the increase of substrate temperature enhances the crystallinity in the film