Staying in Germany
Having graduated from a German university or college, you may stay up to 18 months in Germany seeking employment corresponding to your qualification. Successful completion of a doctorate is also a university or college degree.
Permission for seeking employment in Germany for 18 months after a German university or college study programme is not suspended by short stays in a foreign country.
If you want to work self-employed after graduating from a German university or college, you can be granted a residence permit to work self-employed under facilitated conditions provided that the desired activity relates to the obtained university or college degree.
For more detailed information please check the websites of the Ausländerbehörde Berlin.