| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Tuesday Sessions |
| Session EM-TuA |
| Session: | High-k Dielectrics for MOSFETs Part 2 |
| Presenter: | Jun Nakamura, The University of Electro-Communications (UEC-Tokyo), Japan |
| Authors: | J. Nakamura, The University of Electro-Communications (UEC-Tokyo), Japan M. Tamura, The University of Electro-Communications (UEC-Tokyo), Japan |
| Correspondent: | Click to Email |
Ge-based metal-oxide-semiconductor (MOS) devices are focused as complementary-MOS devices for the next-generation in the post-Si technology. However, the dielectric properties of GeO2 gate ultrathin films have not been clarified yet in detail. Our purpose is to clarify the spatial variation of the local dielectric constant for the GeO2 thin films using first-principles ground-state calculations in external electric fields [1,2]. In particular, we reveal the local profile of the dielectric constant near the oxygen vacancy in the film, focusing on the crystal phase dependence.
We have adopted quartz (0001) and rutile (001) films with/without oxygen vacancies, in which Ge atoms at the topmost surfaces are terminated with H atoms. We have evaluated the optical and the static dielectric constants that are attributed to the electronic polarization and both the lattice and electronic polarizations, respectively.
From the local profile of the dielectric constants for the ideal films, it has been clarified that the dielectric constants change gradually from the surface and approach constant values at the center of the film. Such features have also been confirmed for the Si and SiO2 films [1,2]. The dielectric constant for the defective model of the quartz film becomes larger locally “at” the oxygen vacancy site compared with that for the ideal model, but at “adjoining” oxygen sites to the vacancy for the rutile film. Such features stem from the difference in the fashion of the chemical bonding between Ge and O atoms: The dielectric constant for the defective quartz model becomes large at the vacancy site where the covalent Ge-Ge bonding is formed. For the rutile, on the other hand, the Ge-O bondings surrounding the vacancy site are softened because of their less ionic character, which results in the larger displacement in external electric fields, leading to the larger lattice polarization around the vacancy.
[1] J. Nakamura et al., J. Appl. Phys. 99, 054309 (2006); Appl. Phys. Lett. 89, 053118 (2006)
[2] S. Wakui et al., J. Vac. Sci. Technol. B 26, 1579 (2008); ibid 27, 2020 (2009).