A long term and comprehensive study has been performed to identify the origin of the Ge center in AlGaAs grown by organometallic vapor phase epitaxy. With a series of deductive investigations, AsH3 gas has been undoubtedly identified as the source of the Ge contamination. Depending on the AsH3 quality, one to two orders of magnitude of difference in Ge trap densities has been observed. Long-term observations indicate fairly constant Ge content throughout most of the AsH3 tank lifetime. Different impurity getters were attempted to remove the Ge contaminant. While most getters can eliminate the oxygen-related defects in AlGaAs, no getters were able to remove the Ge DX center.