Universidad de Valladolid

Universidad de Valladolid

Multiscale modeling approach to defect engineering for extending semiconductor applications

Project TEC2014-60694-P, funded by Ministerio Economia logoLogo FEDER

The goal of Semiconductor defect engineering is to design processing conditions to obtain desired defect distributions in order to enhance positive macroscopic effects and minimize the presence of defects that results in device degradation, so that appropriate operation of integrated circuits and devices is achieved. This project is focused on Si and Ge ion implanted defects that introduce midgap levels responsible for electronic characteristics (photoluminescence signals, leakage currents, hole traps) and structural modifications (honeycombs in Ge). This project has two main objectives. Firstly, to provide the theoretical understanding for stablishing control of defects in Si and Ge by systematically exploring the role of mechanical strain (local or external). Secondly, the development of defect engineering strategies with special significance in the power consumption of electronic devices (defects induce the appearance of leakage currents), in the energy conversion efficiency in solar cells (defects act as carrier traps), in the reinforcement of defects responsible for the photoluminescence lines for optoelectronic applications, or in the formation of nanostructured layers such as honeycombs in Ge due to the evolution of defects generated during ion implantation.

In this work we will use a multi-scale simulation scheme in which we combine ab initio, molecular dynamics, and kinetic Monte Carlo techniques to obtain fundamental defect properties, and to reach space and time scales directly comparable to experiments. This project intends to perform a systematic analysis of the effect of strain on defect evolution, considering not only external pressures but also the local strain fields generated by defects themselves that can modify the structural and energetic characteristics of surrounding defects. The outcome of this project can result in the revision of defect evolution theories, in the clarification of apparently contradictory experimental results, in the differentiation of the defect behavior at nanostructures (where the surface can relax the strain induced by defects) from their behavior in bulk, in the development of more predictive models for technological processes, and in the definition of control variables for the optimization of processes and devices for relevant applications. Some particular aspects that will be addressed in the project are (i) the assignment of particular defects to photoluminescence lines, (ii) the description of the formation mechanisms and the atomic structure of extended interstitially defects, (iii) the clarification of the role of Ge and C on the defect evolution in crystalline Si and in the behavior of hole traps in amorphous Si, (iv) the elucidation of the role of vacancies in the formation of nanostructures in amorphous Ge. This work will be focused in Si and Ge, and in particular applications. Nevertheless, the methodology and results can be extended to other materials and applications.

The tasks of the project are distributed along 3 years, and they will be carried out by a PhD student and 5 doctors with demonstrated experience in different simulation techniques and in the study of materials and processes relevant in process technology.