Atomic and Electronic Structure of Interfaces in Materials Systems for Future Semiconductor Devices

Abstract

Because of the intrinsic limits of the Si/SiO₂ based industry, there is a great trend towards the monolithic integration of new materials into already well developed silicon technology. Having lasted for several decades now, downscaling reaches the limit, in which a critical device dimension approaches the size of one atom. At this level of the miniaturization, it is not the bulk material, but the interface between the two materials that what controls the properties of the resulting optoelectronic device. Thus, the characterization of precise atomic arrangements at different interfaces and the influence of these arrangements on the optoelectronic properties of interfaces is required. Therefore, in this study, a combination of scanning transmission electron microscopy (STEM) techniques and density functional theory calculations was used as a research tool for the characterization of interfaces. The STEM instruments used for the study were equipped with prototypes of spherical aberration correctors, enabling to achieve the highest resolution currently available both in space and energy. The combination of experimental and theoretical methods was applied to study interfaces between Si/GaAs, Si/Ge, Ge/SiO₂, Si/HfO₂ and Si/Al₂O₃. As the result of the present research, a new dislocation configuration at the Si/GaAs interface was reported for the first time. The influence of this dislocation structure on the electrical properties of the Si/GaAs interface was analyzed. Also, the transition from Si to GaAs and from Si to Ge at corresponding interfaces was described with atomic precision. For the first time, the interface between Ge and SiO₂ was shown to have 'ideal' characteristics (chemical abruptness and sharpness). This indicates the potential, both for a more successful use of Ge in high-speed devices and for advances in interface engineering to enhance performance in electronic devices. The features of Si/HfO₂ and Si/Al₂O₃ interfaces, namely the distribution and bonding of Si and Hf across the interface, and the formation of charged SiO₂ islands at the Si/Al₂O₃ interface were also studied. These results for materials systems show the significance of a basic understanding of the atomic structures of interfaces for a rapid development of new electronic devices.