Multiscale Materials Modeling Group
Universidad de Valladolid
Project TEC2017-86150-P, funded by 
The development of the deposition technology has been key for the advance in the fabrication of integrated circuits. To reach further improvements on device scaling beyond the year 2020 it is expected that SiGe layers with a high Ge content will be an active part of devices. In this case, the lattice misfit between Si and Ge makes the fabrication of atomically flat layers a huge challenge, since clusters of atoms (islands) are usually formed during the process, which have a negative effect on the performance of conventional devices. However, these 3D structures can be used to create quantum dots in photonic devices, pyramids to improve the optic absorption, sensors, etc. As the dimension of integrated circuits and other devices are shrinking, the tolerances of thin film fabrication processes are increasingly stringent. The atomistic modeling can provide a detailed description of the process, but the knowledge of the physics mechanisms involved (strain accommodation, morphological evolution, interdiffusion, etc.) is still incomplete. This is the main bottleneck to minimize the growth of defects (dislocations, roughness, island formation, etc.) that limit the development of this technology, or to optimize their formation for the development of new devices based on SiGe nanostructures.
This project aims to provide a detailed atomistic view of the SiGe growth modes on Si and the theoretical bases for the development of predictive atomistic models of SiGe epitaxial growth, by identifying the most relevant atomic mechanisms and by quantifying the parameters that govern them. To face these goals atomistic simulations techniques will be used (classical molecular dynamics and ab initio techniques). We propose to make a systematic analysis and a quantitative characterization of the parameters that are necessary to define the morphological evolution of the surface during the SiGe growth on a Si substrate. Some particular aspects that will be addressed include the diffusion mechanisms (on terraces, around islands, between steps and the different layers) and the energies for the interaction between species in different morphologies, paying a special attention to the local strain in all of them. The SiGe on Si system has a high technological relevance, but it is also a paradigm of the strain effect on different epitaxial growth modes, and therefore its study will also contribute to a better understanding of other materials and alloys.