Modulation-Acceptor Doped SiGe-Alloys for Junctionless FETs

In an Austrian-German collaboration between TU Wien, the Johannes Kepler University Linz, and the TU Bergakademie Freiberg, innovative transistors with remotely coupled conductivity control are to be investigated and demonstrated experimentally. The smaller electronic components get, the more complex their manufacturing and the controlled adjustment of their conductivity become. Conventional electronic devices, such as transistors, are based on doped semiconductor materials. To achieve this, semiconductors such as silicon or germanium are specifically modified by adding a small amount of impurity atoms, called dopants. This process, which has been continuously optimized over decades, is reaching its limits with nanometer-scale devices, as random fluctuations in doping have a significant impact on individual transistor properties. The approach taken in this research project is to investigate a novel form of doping known as modulation acceptor doping. There the properties of the semiconductor are to be remotely adjusted. Further on, this project targets the experimental demonstration and evaluation of this effect in nanometer-scale transistor structures. To this end, transistor nanostructures built of the highly relevant semiconductor material silicon germanium (SiGe) are considered. In an exchange with the surrounding isolation layer the semiconductor channel material is to be flooded with high densities of charge carriers. As the process occurs remotely, the semiconductor material and the channel mobility shall not be impaired through impurity scattering, distinctly different to the case in impurity doping. The consortium combines globally recognized expertise in three groups interacting with each other: Assoc. Prof. Dr. Moritz Brehm (JKU Linz) is an expert in the controlled crystal growth of silicon- germanium using molecular beam epitaxy and provides the semiconductor channels and heterostructures; Prof. Dr. Daniel Hiller (TU Freiberg) is an expert in interface physics and oxide nanolaminates and provides the remotely coupled conductivity control; Univ.Prof. Dr. Walter M. Weber is an expert in semiconductor devices and nanotechnology and integrates the transistors and test structures in a clean room environment and characterizes these electrically. The experimental work carried out by the German-Austrian collaboration is accompanied by computer simulations in cooperation with Dr. Dirk König from the Australian National University (ANU) in Canberra, Australia, with regard to the theory and validation of the results. The research is highly relevant to semiconductor research, the scaling and energy efficiency of semiconductor circuits in chips. In addition, the findings are important for the operation of quantum chips, where the control and readout electronics of quantum bits (qubits) are required at temperatures close to the absolute minimum, i.e., at cryogenic temperatures, where conventional doping fails due to charge carrier freeze-out.