We report the observation of ultrafast capture of free electrons (n-Ge:Sb:Ga) and holes (p-Ge:Ga:Sb) in moderately doped (net concentration > 2×10^15/cm3) Ge with high compensation, up to 50%. The typical range of the relaxation times for photoinduced (far-infrared photo- ionization) transmittance is in the range of 20-300 ps dependent on the sample characteristics and the far-infrared light intensity. Measurements of the photoinduced decay have been carried out by a contactless pump-probe technique at the infrared free electron laser facility at HZDR, Dresden. The observed relaxation times of free charge carriers are up to two orders of magnitude shorter than the ~ 2 ns response time observed in the photoconductive response of neutron transmutation doped isotope-fixed compensated p-Ge:Ga:Se:As. This indicates the potential for very fast broad band detection of infrared pulses by extrinsic photoconductive germanium detectors with optimized doping, compensation, geometry and an appropriate electrical readout circuit
