I am interested if teaching is a part of duties for people employed on the positions funded by the German Research Foundation (SFBs in particular). To the best of my knowledge, these are pure research positions. However, what is the legal status?
As far as I know, you shall not teach within your contract as doctoral researcher in a DFG funded SFB. The reason is simple: There is a project proposal and the DFG gives money to do the work that is described in the proposal. If the proposal does say that the PhD student should work on the research project (and does not say that teaching is part of the job) you shall do that and nothing else.
However, there are several caveats: This applies to all the part of your job that is funded by the SFB. It is not unusual that your position has mixed funding, e.g. 50% comes from an SFB (or another DFG project) and 50% comes from something else. You should not do any teaching in your 50% that are related to the research project, what you do in the rest of the time is another matter. I also know that it is indeed common that PhD students in DFG funded research projects actually do teach somehow (e.g. as a TA). (Probably it is worth noting that PhD students who are funded directly by the university always have teaching duties in Germany.) Maybe this is allowed under some circumstances, but I could not find any regulations by the DFG that are explicit about this. The only thing I found is this part:
4.9.2 Eigene Stelle Personen, die mit einer Eigenen Stelle durch die DFG gefördert werden, sind verpflichtet, sich mit ihrer vollen Arbeitszeit dem in der Bewilligung genannten Projekt zu widmen. Darüber hinausgehende Tätigkeiten für die aufnehmende wissenschaftliche Einrichtung (insbesondere Lehrtätigkeiten oder projektfremde Dienstleistungen wie beispielsweise klinische Routinetätigkeiten sowie die Mitwirkung bei der Patientenversorgung) sind im Rahmen der von der DFG finanzierten Stelle nicht zulässig. Solche Tätigkeiten können außerhalb der regelmäßigen wöchentlichen Arbeitszeit der von der DFG finanzierten Stelle im Rahmen des für die wissenschaftliche Einrichtung geltenden Nebentätigkeitsrechts ausgeübt werden.
This is a quote from the "Verwendungsrichtlinien" of the DFG an applies in the case where you write a proposal to fund your own position. The relevent sentence says that no teaching or non-project related service is allowed.
In general, teaching duties are not required as a condition of SFBs and related programs if the funding covers all of the student’s salary. However, in many fields, the position that they receive might only be 50% or 70% of a TV-L 13 (the “standard position” for calculating graduate student salaries in the German government wage scale). The remainder of their time in principle could be used for teaching to make up the salary difference.
In addition, there is often the expectation that everybody in a professor’s group will make some contribution to teaching efforts unless their funding explicitly prohibits it. But this is a matter of “internal culture” and not something imposed or expected by the DFG.