Sciences Naturelles et de l'Ingénieur

Atomic-Scale Investigation of the Defect Levels at Ge and III-V Interfaces

High mobility materials such as Ge and GaAs (or InGaAs) are presently being investigated as possible solutions for addressing the post-silicon era in nanoelectronics. However, so far, the interfaces between these semiconductors and suitable gate-oxides show excessive amounts of defect states, which have resisted straightforward passivation techniques. In this project, a first-principles simulation study is proposed to identify the origin and the nature of the defects associated to the observed defect levels. The study rests on structural generation techniques based on ab initio molecular dynamics and on hybrid functional methods, thereby allowing for a meaningful comparison with experimental data for band alignments and defect energy levels. This study encompasses the generation of several atomistic models of interfaces, involving either Ge and III-V materials as semiconductor and disordered Al2O3 or HfO2 as gate oxides. Particular attention will be devoted to defects revealed by the ab initio molecular dynamics simulations, but specific ad-hoc created defect structures will also be considered in order to understand the effect of standard passivation schemes based on, e.g. H, S, or Se. The present project targets the comprehensive understanding of typical defects occurring at these interfaces, an ineluctable step for allowing the transition to the post-silicon era in nanoelectronics.