Many Body Perturbation Theory Study of Dopants and Defects in Crystalline and Amorphous GeO2
Résumé
The quest for high-mobility MOSFET channel material has led electronic material researchers to replace silicon by germanium in advanced technologies. This field of research has been the subject of many studies in recent years (see for example [1]). One of the main problem of the rise of germanium as a possible material is its oxide, GeO2, and its interface with the latter, because of the larger defects density in Ge:GeO2 than in Si:SiO2. In this study, we performed first principles calculations on defects and dopants in crystalline and amorphous GeO2. Calculations based on the Density Functional Theory (DFT) using the Local Density Approximation (LDA) are performed through the PWscf code from the Quantum ESPRESSO distribution [2]. These calculations allow us to have access to the atomic configurations of defects and dopants and to their energy properties. Starting from the wavefunctions and from the atomic configurations obtained in DFT, we use the SaX code version 2.0 [3] to apply the GW approximation to obtain a right value of the band gap and to evaluate the effects of point defects, dopants and impurities on the electronic properties of GeO2. Finally, the optical properties (particularly the absorption spectra) of pure and doped GeO2 are given including excitonic effects with resolution of the Bethe-Salpeter equation (BSE). A particular attention will be given to the levels introduced by dopants and defects in the electronic structure of Germania and their effects in terms of charge capture will be discussed. We already successfully applied this methodology to oxygen vacancies in pure and Germanium doped silica [4] and the results obtained will be discussed and compared to the results coming from this previous study and from literature. [1] M. Houssa, A. Satta, E. Simoen, B. De Jaeger, M. Caymax, M. Meuris, and M. Heyns, in Germanium Based Technologies: From Materials to Devices, edited by C. Claeys and E. Simoen Elsevier, Amsterdam, 2007, p. 233. [2] P. Giannozzi et al., J. Phys. Condens.Matter, 21, 395502 (2009). [3] L. Martin-Samos and G. Bussi, Comp. Phys. Com., 180, 1416 (2009). [4] N. Richard et al., J. Phys.: Condens. Matter, 25, 335502 (2013).